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Quickbook: Merge from trunk.
Includes blocks in lists fixes, and some documentation changes. [SVN r77347]
This commit is contained in:
Daniel James
commit
bd926863ae
@ -129,6 +129,8 @@ particular member type does not need to concern itself with the integer.</p>
|
||||
<h2><a name="synopsis">Synopsis</a></h2>
|
||||
|
||||
<blockquote><pre>
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#include <type_traits> <i>// exposition only</i>
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#ifndef BOOST_BASE_FROM_MEMBER_MAX_ARITY
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#define BOOST_BASE_FROM_MEMBER_MAX_ARITY 10
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#endif
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@ -139,6 +141,11 @@ class boost::base_from_member
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protected:
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MemberType member;
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#if <i>C++2011 is in use</i>
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template< typename ...T >
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explicit constexpr base_from_member( T&& ...x )
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noexcept( std::is_nothrow_constructible<MemberType, T...>::value );
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#else
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base_from_member();
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template< typename T1 >
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@ -154,6 +161,7 @@ protected:
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typename T10 >
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base_from_member( T1 x1, T2 x2, T3 x3, T4 x4, T5 x5, T6 x6, T7 x7,
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T8 x8, T9 x9, T10 x10 );
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#endif
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||||
};
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</pre></blockquote>
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||||
@ -166,13 +174,29 @@ value of zero if it is omitted. The class template has a protected
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data member called <var>member</var> that the derived class can use
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for later base classes (or itself).</p>
|
||||
|
||||
<p>There is a default constructor and several constructor member
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templates. These constructor templates can take as many arguments
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(currently up to ten) as possible and pass them to a constructor of
|
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the data member. Since C++ does not allow any way to explicitly state
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<p>If the appropriate features of C++2011 are present, there will be a single
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constructor template. It implements "perfect forwarding" to the best
|
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constructor call of <code>member</code> (if any). The constructor template is
|
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marked both <code>constexpr</code> and <code>explicit</code>. The former will
|
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be ignored if the corresponding inner constructor call (of <code>member</code>)
|
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does not have the marker. The latter binds the other way; always taking
|
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effect, even when the inner constructor call does not have the marker. The
|
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constructor template propagates the <code>noexcept</code> status of the inner
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constructor call. (The constructor template has a trailing parameter with a
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default value that disables the template when its signature is too close to the
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signatures of the automatically-defined non-template copy- and/or
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move-constructors of <code>base_from_member</code>.)</p>
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|
||||
<p>On earlier-standard compilers, there is a default constructor and several
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constructor member templates. These constructor templates can take as many
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arguments (currently up to ten) as possible and pass them to a constructor of
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the data member.</p>
|
||||
|
||||
<p>Since C++ does not allow any way to explicitly state
|
||||
the template parameters of a templated constructor, make sure that
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the arguments are already close as possible to the actual type used in
|
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the data member's desired constructor.</p>
|
||||
the data member's desired constructor. Explicit conversions may be
|
||||
necessary.</p>
|
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|
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<p>The <var>BOOST_BASE_FROM_MEMBER_MAX_ARITY</var> macro constant specifies
|
||||
the maximum argument length for the constructor templates. The constant
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@ -180,7 +204,7 @@ may be overridden if more (or less) argument configurations are needed. The
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||||
constant may be read for code that is expandable like the class template and
|
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needs to maintain the same maximum size. (Example code would be a class that
|
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uses this class template as a base class for a member with a flexible set of
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constructors.)</p>
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constructors.) This constant is ignored when C++2011 features are present.</p>
|
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<h2><a name="usage">Usage</a></h2>
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||||
@ -323,11 +347,14 @@ constructor argument for <code>pbase0_type</code> is converted from
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argument for <code>pbase2_type</code> is converted from <code>int</code>
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to <code>double</code>. The second constructor argument for
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||||
<code>pbase3_type</code> is a special case of necessary conversion; all
|
||||
forms of the null-pointer literal in C++ also look like compile-time
|
||||
integral expressions, so C++ always interprets such code as an integer
|
||||
when it has overloads that can take either an integer or a pointer. The
|
||||
last conversion is necessary for the compiler to call a constructor form
|
||||
with the exact pointer type used in <code>switcher</code>'s constructor.</p>
|
||||
forms of the null-pointer literal in C++ (except <code>nullptr</code> from
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||||
C++2011) also look like compile-time integral expressions, so C++ always
|
||||
interprets such code as an integer when it has overloads that can take either
|
||||
an integer or a pointer. The last conversion is necessary for the compiler to
|
||||
call a constructor form with the exact pointer type used in
|
||||
<code>switcher</code>'s constructor. (If C++2011's <code>nullptr</code> is
|
||||
used, it still needs a conversion if multiple pointer types can be accepted in
|
||||
a constructor call but <code>std::nullptr_t</code> cannot.)</p>
|
||||
|
||||
<h2><a name="credits">Credits</a></h2>
|
||||
|
||||
@ -360,9 +387,9 @@ with the exact pointer type used in <code>switcher</code>'s constructor.</p>
|
||||
|
||||
<hr>
|
||||
|
||||
<p>Revised: 28 August 2004</p>
|
||||
<p>Revised: 16 February 2012</p>
|
||||
|
||||
<p>Copyright 2001, 2003, 2004 Daryle Walker. Use, modification, and distribution
|
||||
<p>Copyright 2001, 2003, 2004, 2012 Daryle Walker. Use, modification, and distribution
|
||||
are subject to the Boost Software License, Version 1.0. (See accompanying
|
||||
file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or a copy at <<a
|
||||
href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>>.)</p>
|
||||
|
||||
31
identity_type/doc/Jamfile.v2
Normal file
31
identity_type/doc/Jamfile.v2
Normal file
@ -0,0 +1,31 @@
|
||||
|
||||
# Copyright (C) 2009-2012 Lorenzo Caminiti
|
||||
# Distributed under the Boost Software License, Version 1.0
|
||||
# (see accompanying file LICENSE_1_0.txt or a copy at
|
||||
# http://www.boost.org/LICENSE_1_0.txt)
|
||||
# Home at http://www.boost.org/libs/utility/identity_type
|
||||
|
||||
import quickbook ;
|
||||
using boostbook ;
|
||||
|
||||
doxygen reference : ../../../../boost/utility/identity_type.hpp
|
||||
: <reftitle>"Reference"
|
||||
<doxygen:param>PREDEFINED="DOXYGEN"
|
||||
<doxygen:param>QUIET=YES
|
||||
<doxygen:param>WARN_IF_UNDOCUMENTED=NO
|
||||
<doxygen:param>HIDE_UNDOC_MEMBERS=YES
|
||||
<doxygen:param>HIDE_UNDOC_CLASSES=YES
|
||||
<doxygen:param>ALIASES=" Params=\"<b>Parameters:</b> <table border="0">\" Param{2}=\"<tr><td><b><tt>\\1</tt></b></td><td>\\2</td></tr>\" EndParams=\"</table>\" Returns=\"<b>Returns:</b>\" Note=\"<b>Note:</b>\" Warning=\"<b>Warning:</b>\" See=\"<b>See:</b>\" RefSect{1}=\"\\xmlonly<link linkend='boost_utility_identitytype.\\1'>\\1</link>\\endxmlonly\" RefSectId{2}=\"\\xmlonly<link linkend='boost_utility_identitytype.\\1'>\\2</link>\\endxmlonly\" RefClass{1}=\"\\xmlonly<computeroutput><classname alt='\\1'>\\1</classname></computeroutput>\\endxmlonly\" RefFunc{1}=\"\\xmlonly<computeroutput><functionname alt='\\1'>\\1</functionname></computeroutput>\\endxmlonly\" RefMacro{1}=\"\\xmlonly<computeroutput><macroname alt='\\1'>\\1</macroname></computeroutput>\\endxmlonly\" "
|
||||
;
|
||||
|
||||
# This target must be called "index" so to generate "index.html" file.
|
||||
xml index : identity_type.qbk : <dependency>reference ;
|
||||
|
||||
boostbook doc : index
|
||||
: <location>html
|
||||
<format>onehtml
|
||||
<xsl:param>toc.section.depth=0
|
||||
<xsl:param>html.stylesheet=../../../../../doc/src/boostbook.css
|
||||
<xsl:param>boost.root=../../../../..
|
||||
;
|
||||
|
||||
237
identity_type/doc/html/index.html
Normal file
237
identity_type/doc/html/index.html
Normal file
@ -0,0 +1,237 @@
|
||||
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Boost.Utility/IdentityType 1.0.0</title><link rel="stylesheet" type="text/css" href="../../../../../doc/src/boostbook.css"><meta name="generator" content="DocBook XSL Stylesheets V1.76.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="chapter" title="Boost.Utility/IdentityType 1.0.0"><div class="titlepage"><div><div><h2 class="title"><a name="boost_utility_identitytype"></a>Boost.Utility/IdentityType 1.0.0</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Lorenzo</span> <span class="surname">Caminiti <code class="email"><<a class="email" href="mailto:lorcaminiti@gmail.com">lorcaminiti@gmail.com</a>></code></span></h3></div></div><div><p class="copyright">Copyright © 2009-2012 Lorenzo
|
||||
Caminiti</p></div><div><div class="legalnotice" title="Legal Notice"><a name="boost_utility_identitytype.legal"></a><p>
|
||||
Distributed under the Boost Software License, Version 1.0 (see accompanying
|
||||
file LICENSE_1_0.txt or a copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
|
||||
</p></div></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#boost_utility_identitytype.motivation">Motivation</a></span></dt><dt><span class="section"><a href="#boost_utility_identitytype.solution">Solution</a></span></dt><dt><span class="section"><a href="#boost_utility_identitytype.templates">Templates</a></span></dt><dt><span class="section"><a href="#boost_utility_identitytype.abstract_types">Abstract Types</a></span></dt><dt><span class="section"><a href="#boost_utility_identitytype.annex__usage">Annex: Usage</a></span></dt><dt><span class="section"><a href="#boost_utility_identitytype.annex__implementation">Annex:
|
||||
Implementation</a></span></dt><dt><span class="section"><a href="#reference">Reference</a></span></dt></dl></div><p>
|
||||
This library allows to wrap type expressions within round parenthesis so they
|
||||
can be passed to macros even when they contain commas.
|
||||
</p><div class="section boost_utility_identitytype_motivation" title="Motivation"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="boost_utility_identitytype.motivation"></a><a class="link" href="#boost_utility_identitytype.motivation" title="Motivation">Motivation</a></h2></div></div></div><p>
|
||||
Consider the following macro which declares a variable named <code class="computeroutput"><span class="identifier">var</span></code><code class="literal"><span class="emphasis"><em>n</em></span></code>
|
||||
with the specified <code class="literal"><span class="emphasis"><em>type</em></span></code> (see also
|
||||
<a href="../../test/var_error.cpp" target="_top"><code class="literal">var_error.cpp</code></a>):
|
||||
</p><p>
|
||||
</p><pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">VAR</span><span class="special">(</span><span class="identifier">type</span><span class="special">,</span> <span class="identifier">n</span><span class="special">)</span> <span class="identifier">type</span> <span class="identifier">var</span> <span class="error">#</span><span class="preprocessor"># n</span>
|
||||
|
||||
<span class="identifier">VAR</span><span class="special">(</span><span class="keyword">int</span><span class="special">,</span> <span class="number">1</span><span class="special">);</span> <span class="comment">// OK.</span>
|
||||
<span class="identifier">VAR</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>,</span> <span class="number">2</span><span class="special">);</span> <span class="comment">// Error.</span>
|
||||
</pre><p>
|
||||
</p><p>
|
||||
The first macro invocation works correctly declaring a variable named <code class="computeroutput"><span class="identifier">var1</span></code> of type <code class="computeroutput"><span class="keyword">int</span></code>.
|
||||
However, the second macro invocation fails generating a preprocessor error
|
||||
similar to the following:
|
||||
</p><pre class="programlisting">error: macro "VAR" passed 3 arguments, but takes just 2
|
||||
</pre><p>
|
||||
That is because the <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span></code> type passed as the first macro parameter
|
||||
contains a comma <code class="computeroutput"><span class="special">,</span></code> not wrapped
|
||||
by round parenthesis <code class="computeroutput"><span class="special">()</span></code>. The preprocessor
|
||||
interprets that unwrapped comma as a separation between macro parameters concluding
|
||||
that a total of three (and not two) parameters are passed to the macro in the
|
||||
following order:
|
||||
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
|
||||
<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="keyword">int</span></code>
|
||||
</li><li class="listitem">
|
||||
<code class="computeroutput"><span class="keyword">char</span><span class="special">></span></code>
|
||||
</li><li class="listitem">
|
||||
<code class="computeroutput"><span class="number">2</span></code>
|
||||
</li></ol></div><p>
|
||||
Note that, differently from the compiler, the preprocessor only recognizes
|
||||
round parameters <code class="computeroutput"><span class="special">()</span></code>. Angular
|
||||
<code class="computeroutput"><span class="special"><></span></code> or squared <code class="computeroutput"><span class="special">[]</span></code> parenthesis are not used by the preprocessor
|
||||
when parsing the macro parameters.
|
||||
</p></div><div class="section boost_utility_identitytype_solution" title="Solution"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="boost_utility_identitytype.solution"></a><a class="link" href="#boost_utility_identitytype.solution" title="Solution">Solution</a></h2></div></div></div><p>
|
||||
In some cases, it might be possible to workaround this issue by avoiding to
|
||||
pass the type expression to the macro all together. For example, in some cases
|
||||
a <code class="computeroutput"><span class="keyword">typedef</span></code> can be used to specify
|
||||
the type expression with the commas outside the macro (see also <a href="../../test/var.cpp" target="_top"><code class="literal">var.cpp</code></a>):
|
||||
</p><p>
|
||||
</p><pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">></span> <span class="identifier">map_type</span><span class="special">;</span>
|
||||
<span class="identifier">VAR</span><span class="special">(</span><span class="identifier">map_type</span><span class="special">,</span> <span class="number">3</span><span class="special">);</span> <span class="comment">// OK.</span>
|
||||
</pre><p>
|
||||
</p><p>
|
||||
When this is not possible or desired (e.g., see the function template <code class="computeroutput"><span class="identifier">f</span></code> in the section below), the library header
|
||||
<code class="computeroutput"><a class="link" href="#header.boost.utility.identity_type_hpp" title="Header <boost/utility/identity_type.hpp>">boost/utility/identity_type.hpp</a></code>
|
||||
defines a macro <code class="computeroutput"><a class="link" href="#BOOST_IDENTITY_TYPE" title="Macro BOOST_IDENTITY_TYPE">BOOST_IDENTITY_TYPE</a></code>
|
||||
which can be used to workaround the issue while keeping the type expression
|
||||
as one of the macro parameters (see also <a href="../../test/var.cpp" target="_top"><code class="literal">var.cpp</code></a>).
|
||||
</p><p>
|
||||
</p><pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">utility</span><span class="special">/</span><span class="identifier">identity_type</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
|
||||
|
||||
<span class="identifier">VAR</span><span class="special">(</span><span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>)),</span> <span class="number">4</span><span class="special">);</span> <span class="comment">// OK.</span>
|
||||
</pre><p>
|
||||
</p><p>
|
||||
This macro expands to an expression that evaluates (at compile-time) to the
|
||||
specified type. The specified type is never split into multiple macro parameters
|
||||
because it is always wrapped by a set of extra round parenthesis <code class="computeroutput"><span class="special">()</span></code>. In fact, a total of two sets of round parenthesis
|
||||
must be used: The parenthesis to invoke the macro <code class="computeroutput"><span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">(...)</span></code> plus the inner parenthesis to wrap the
|
||||
type passed to the macro <code class="computeroutput"><span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((...))</span></code>.
|
||||
</p><p>
|
||||
This macro works on any <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/standards" target="_top">C++03</a>
|
||||
compiler (because it does not use <a href="http://en.wikipedia.org/wiki/Variadic_macro" target="_top">variadic
|
||||
macros</a>). <sup>[<a name="boost_utility_identitytype.solution.f0" href="#ftn.boost_utility_identitytype.solution.f0" class="footnote">1</a>]</sup>
|
||||
</p></div><div class="section boost_utility_identitytype_templates" title="Templates"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="boost_utility_identitytype.templates"></a><a class="link" href="#boost_utility_identitytype.templates" title="Templates">Templates</a></h2></div></div></div><p>
|
||||
This macro must be prefixed by <code class="computeroutput"><span class="keyword">typename</span></code>
|
||||
when used within templates. For example, let's program a macro that declares
|
||||
a function parameter named <code class="computeroutput"><span class="identifier">arg</span></code><code class="literal"><span class="emphasis"><em>n</em></span></code>
|
||||
with the specified <code class="literal"><span class="emphasis"><em>type</em></span></code> (see also
|
||||
<a href="../../test/template.cpp" target="_top"><code class="literal">template.cpp</code></a>):
|
||||
</p><p>
|
||||
</p><pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">ARG</span><span class="special">(</span><span class="identifier">type</span><span class="special">,</span> <span class="identifier">n</span><span class="special">)</span> <span class="identifier">type</span> <span class="identifier">arg</span> <span class="error">#</span><span class="preprocessor"># n</span>
|
||||
|
||||
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">void</span> <span class="identifier">f</span><span class="special">(</span> <span class="comment">// Prefix macro with `typename` in templates.</span>
|
||||
<span class="identifier">ARG</span><span class="special">(</span><span class="keyword">typename</span> <span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">T</span><span class="special">>)),</span> <span class="number">1</span><span class="special">)</span>
|
||||
<span class="special">)</span> <span class="special">{</span>
|
||||
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">arg1</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
|
||||
<span class="special">}</span>
|
||||
</pre><p>
|
||||
</p><p>
|
||||
</p><pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">></span> <span class="identifier">a</span><span class="special">;</span>
|
||||
<span class="identifier">a</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">=</span> <span class="char">'a'</span><span class="special">;</span>
|
||||
|
||||
<span class="identifier">f</span><span class="special"><</span><span class="keyword">char</span><span class="special">>(</span><span class="identifier">a</span><span class="special">);</span> <span class="comment">// OK...</span>
|
||||
<span class="comment">// f(a); // ... but error.</span>
|
||||
</pre><p>
|
||||
</p><p>
|
||||
However, note that the template parameter <code class="computeroutput"><span class="keyword">char</span></code>
|
||||
must be manually specified when invoking the function <code class="computeroutput"><span class="identifier">f</span><span class="special"><</span><span class="keyword">char</span><span class="special">>(</span><span class="identifier">a</span><span class="special">)</span></code>. In fact,
|
||||
when the <code class="computeroutput"><a class="link" href="#BOOST_IDENTITY_TYPE" title="Macro BOOST_IDENTITY_TYPE">BOOST_IDENTITY_TYPE</a></code>
|
||||
macro is used to wrap a function template parameter, the template parameter
|
||||
can no longer be automatically deduced by the compiler form the function call
|
||||
as in <code class="computeroutput"><span class="identifier">f</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</span></code>. <sup>[<a name="boost_utility_identitytype.templates.f0" href="#ftn.boost_utility_identitytype.templates.f0" class="footnote">2</a>]</sup> (This limitation does not apply to class templates because class
|
||||
template parameters must always be explicitly specified.) In other words, without
|
||||
using the <code class="computeroutput"><a class="link" href="#BOOST_IDENTITY_TYPE" title="Macro BOOST_IDENTITY_TYPE">BOOST_IDENTITY_TYPE</a></code>
|
||||
macro, C++ would normally be able to automatically deduce the function template
|
||||
parameter as shown below:
|
||||
</p><p>
|
||||
</p><pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
|
||||
<span class="keyword">void</span> <span class="identifier">g</span><span class="special">(</span>
|
||||
<span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="identifier">T</span><span class="special">></span> <span class="identifier">arg1</span>
|
||||
<span class="special">)</span> <span class="special">{</span>
|
||||
<span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">arg1</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
|
||||
<span class="special">}</span>
|
||||
</pre><p>
|
||||
</p><p>
|
||||
</p><pre class="programlisting"><span class="identifier">g</span><span class="special"><</span><span class="keyword">char</span><span class="special">>(</span><span class="identifier">a</span><span class="special">);</span> <span class="comment">// OK...</span>
|
||||
<span class="identifier">g</span><span class="special">(</span><span class="identifier">a</span><span class="special">);</span> <span class="comment">// ... and also OK.</span>
|
||||
</pre><p>
|
||||
</p></div><div class="section boost_utility_identitytype_abstract_types" title="Abstract Types"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="boost_utility_identitytype.abstract_types"></a><a class="link" href="#boost_utility_identitytype.abstract_types" title="Abstract Types">Abstract Types</a></h2></div></div></div><p>
|
||||
On some compilers (e.g., GCC), using this macro on abstract types (i.e., classes
|
||||
with one or more pure virtual functions) generates a compiler error. This can
|
||||
be worked around by manipulating the type adding and removing a reference to
|
||||
it.
|
||||
</p><p>
|
||||
Let's program a macro that performs a static assertion on a <a href="http://en.wikipedia.org/wiki/Template_metaprogramming" target="_top">Template
|
||||
Meta-Programming</a> (TMP) meta-function (similarly to Boost.MPL <a href="http://www.boost.org/doc/libs/1_36_0/libs/mpl/doc/refmanual/assert.html" target="_top"><code class="computeroutput"><span class="identifier">BOOST_MPL_ASSERT</span></code></a>). The <code class="computeroutput"><a class="link" href="#BOOST_IDENTITY_TYPE" title="Macro BOOST_IDENTITY_TYPE">BOOST_IDENTITY_TYPE</a></code> macro can be used
|
||||
to pass a meta-function with multiple template parameters to the assert macro
|
||||
(so to handle the commas separating the template parameters). In this case,
|
||||
if the meta-function is an abstract type, it needs to be manipulated adding
|
||||
and removing a reference to it (see also <a href="../../test/tmp_assert.cpp" target="_top"><code class="literal">tmp_assert.cpp</code></a>):
|
||||
</p><p>
|
||||
</p><pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">TMP_ASSERT</span><span class="special">(</span><span class="identifier">metafunction</span><span class="special">)</span> <span class="special">\</span>
|
||||
<span class="identifier">BOOST_STATIC_ASSERT</span><span class="special">(</span><span class="identifier">metafunction</span><span class="special">::</span><span class="identifier">value</span><span class="special">)</span>
|
||||
|
||||
<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">b</span><span class="special">></span>
|
||||
<span class="keyword">struct</span> <span class="identifier">abstract</span> <span class="special">{</span>
|
||||
<span class="keyword">static</span> <span class="keyword">const</span> <span class="keyword">bool</span> <span class="identifier">value</span> <span class="special">=</span> <span class="identifier">b</span><span class="special">;</span>
|
||||
<span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">f</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="comment">// Pure virtual function.</span>
|
||||
<span class="special">};</span>
|
||||
|
||||
<span class="identifier">TMP_ASSERT</span><span class="special">(</span>
|
||||
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">remove_reference</span><span class="special"><</span> <span class="comment">// Add and remove</span>
|
||||
<span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((</span> <span class="comment">// reference for</span>
|
||||
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">add_reference</span><span class="special"><</span> <span class="comment">// abstract type.</span>
|
||||
<span class="identifier">abstract</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">true</span><span class="special">></span>
|
||||
<span class="special">>::</span><span class="identifier">type</span>
|
||||
<span class="special">))</span>
|
||||
<span class="special">>::</span><span class="identifier">type</span>
|
||||
<span class="special">);</span>
|
||||
</pre><p>
|
||||
</p></div><div class="section boost_utility_identitytype_annex__usage" title="Annex: Usage"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="boost_utility_identitytype.annex__usage"></a><a class="link" href="#boost_utility_identitytype.annex__usage" title="Annex: Usage">Annex: Usage</a></h2></div></div></div><p>
|
||||
The <code class="computeroutput"><a class="link" href="#BOOST_IDENTITY_TYPE" title="Macro BOOST_IDENTITY_TYPE">BOOST_IDENTITY_TYPE</a></code> macro
|
||||
can be used either when calling a user-defined macro (as shown by the examples
|
||||
so far), or internally in the definition of a user-defined macro (as shown
|
||||
below). When <code class="computeroutput"><a class="link" href="#BOOST_IDENTITY_TYPE" title="Macro BOOST_IDENTITY_TYPE">BOOST_IDENTITY_TYPE</a></code>
|
||||
is used in the user macro definition, the call of the user macro will only
|
||||
have to specify the extra parenthesis (see also <a href="../../test/tmp_assert.cpp" target="_top"><code class="literal">tmp_assert.cpp</code></a>):
|
||||
</p><p>
|
||||
</p><pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">TMP_ASSERT_PAREN</span><span class="special">(</span><span class="identifier">parenthesized_metafunction</span><span class="special">)</span> <span class="special">\</span>
|
||||
<span class="comment">/* use `BOOST_IDENTITY_TYPE` in macro definition instead of invocation */</span> <span class="special">\</span>
|
||||
<span class="identifier">BOOST_STATIC_ASSERT</span><span class="special">(</span><span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">(</span><span class="identifier">parenthesized_metafunction</span><span class="special">)::</span><span class="identifier">value</span><span class="special">)</span>
|
||||
|
||||
<span class="comment">// Specify only extra parenthesis `((...))`.</span>
|
||||
<span class="identifier">TMP_ASSERT_PAREN</span><span class="special">((</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_const</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">></span> <span class="keyword">const</span><span class="special">>));</span>
|
||||
<span class="comment">// Specify both the extra parenthesis `((...))` and `BOOST_IDENTITY_TYPE` macro.</span>
|
||||
<span class="identifier">TMP_ASSERT</span><span class="special">(</span><span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_const</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">></span> <span class="keyword">const</span><span class="special">>)));</span>
|
||||
</pre><p>
|
||||
</p><p>
|
||||
However, note that the user will <span class="emphasis"><em>always</em></span> have to specify
|
||||
the extra parenthesis even when the macro parameters contain no comma:
|
||||
</p><p>
|
||||
</p><pre class="programlisting"><span class="identifier">TMP_ASSERT_PAREN</span><span class="special">((</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_const</span><span class="special"><</span><span class="keyword">int</span> <span class="keyword">const</span><span class="special">>));</span> <span class="comment">// Always extra `((...))`.</span>
|
||||
<span class="identifier">TMP_ASSERT</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_const</span><span class="special"><</span><span class="keyword">int</span> <span class="keyword">const</span><span class="special">>);</span> <span class="comment">// No extra `((...))` and no macro.</span>
|
||||
</pre><p>
|
||||
</p><p>
|
||||
In some cases, using <code class="computeroutput"><a class="link" href="#BOOST_IDENTITY_TYPE" title="Macro BOOST_IDENTITY_TYPE">BOOST_IDENTITY_TYPE</a></code>
|
||||
within the user macro definition might provide the best syntax for the user.
|
||||
For example, this is the case for <code class="computeroutput"><span class="identifier">BOOST_MPL_ASSERT</span></code>
|
||||
because the majority of template meta-programming expressions contain unwrapped
|
||||
commas so it is less confusing for the user to always specify the extra parenthesis
|
||||
<code class="computeroutput"><span class="special">((...))</span></code> instead of using <code class="computeroutput"><a class="link" href="#BOOST_IDENTITY_TYPE" title="Macro BOOST_IDENTITY_TYPE">BOOST_IDENTITY_TYPE</a></code>:
|
||||
</p><pre class="programlisting"><span class="identifier">BOOST_MPL_ASSERT</span><span class="special">((</span> <span class="comment">// Natural syntax.</span>
|
||||
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">mpl</span><span class="special">::</span><span class="identifier">and_</span><span class="special"><</span>
|
||||
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_const</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span>
|
||||
<span class="special">,</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_reference</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span>
|
||||
<span class="special">></span>
|
||||
<span class="special">));</span>
|
||||
</pre><p>
|
||||
However, in other situations it might be preferable to not require the extra
|
||||
parenthesis in the common cases and handle commas as special cases using <code class="computeroutput"><a class="link" href="#BOOST_IDENTITY_TYPE" title="Macro BOOST_IDENTITY_TYPE">BOOST_IDENTITY_TYPE</a></code>. For example, this
|
||||
is the case for <a href="http://www.boost.org/libs/local_function" target="_top"><code class="computeroutput"><span class="identifier">BOOST_LOCAL_FUNCTION</span></code></a> for which always
|
||||
requiring the extra parenthesis <code class="computeroutput"><span class="special">((...))</span></code>
|
||||
around the types would lead to an unnatural syntax for the local function signature:
|
||||
</p><pre class="programlisting"><span class="keyword">int</span> <span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span> <span class="special">((</span><span class="keyword">int</span><span class="special">&))</span> <span class="identifier">x</span><span class="special">,</span> <span class="special">((</span><span class="keyword">int</span><span class="special">&))</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">{</span> <span class="comment">// Unnatural syntax.</span>
|
||||
<span class="keyword">return</span> <span class="identifier">x</span> <span class="special">+</span> <span class="identifier">y</span><span class="special">;</span>
|
||||
<span class="special">}</span> <span class="identifier">BOOST_LOCAL_FUNCTION_NAME</span><span class="special">(</span><span class="identifier">add</span><span class="special">)</span>
|
||||
</pre><p>
|
||||
Instead requiring the user to specify <code class="computeroutput"><a class="link" href="#BOOST_IDENTITY_TYPE" title="Macro BOOST_IDENTITY_TYPE">BOOST_IDENTITY_TYPE</a></code>
|
||||
only when needed allows for the more natural syntax <code class="computeroutput"><span class="identifier">BOOST_LOCAL_FUNCTION</span><span class="special">(</span><span class="keyword">int</span><span class="special">&</span>
|
||||
<span class="identifier">x</span><span class="special">,</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">y</span><span class="special">)</span></code> in the common cases when the parameter types
|
||||
contain no comma.
|
||||
</p></div><div class="section boost_utility_identitytype_annex__implementation" title="Annex: Implementation"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="boost_utility_identitytype.annex__implementation"></a><a class="link" href="#boost_utility_identitytype.annex__implementation" title="Annex: Implementation">Annex:
|
||||
Implementation</a></h2></div></div></div><p>
|
||||
The implementation of this library macro is equivalent to the following: <sup>[<a name="boost_utility_identitytype.annex__implementation.f0" href="#ftn.boost_utility_identitytype.annex__implementation.f0" class="footnote">3</a>]</sup>
|
||||
</p><pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">function_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
|
||||
|
||||
<span class="preprocessor">#define</span> <span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">(</span><span class="identifier">parenthesized_type</span><span class="special">)</span> <span class="special">\</span>
|
||||
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">function_traits</span><span class="special"><</span><span class="keyword">void</span> <span class="identifier">parenthesized_type</span><span class="special">>::</span><span class="identifier">arg1_type</span>
|
||||
</pre><p>
|
||||
Essentially, the type is wrapped between round parenthesis <code class="computeroutput"><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span>
|
||||
<span class="keyword">char</span><span class="special">>)</span></code>
|
||||
so it can be passed as a single macro parameter even if it contains commas.
|
||||
Then the parenthesized type is transformed into the type of a function returning
|
||||
<code class="computeroutput"><span class="keyword">void</span></code> and with the specified type
|
||||
as the type of the first and only argument <code class="computeroutput"><span class="keyword">void</span>
|
||||
<span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">char</span><span class="special">>)</span></code>. Finally, the type of the first argument
|
||||
<code class="computeroutput"><span class="identifier">arg1_type</span></code> is extracted at compile-time
|
||||
using the <code class="computeroutput"><span class="identifier">function_traits</span></code> meta-function
|
||||
therefore obtaining the original type from the parenthesized type (effectively
|
||||
stripping the extra parenthesis from around the specified type).
|
||||
</p></div><div class="section reference" title="Reference"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="reference"></a>Reference</h2></div></div></div><div class="section header_boost_utility_identity_type_hpp" title="Header <boost/utility/identity_type.hpp>"><div class="titlepage"><div><div><h3 class="title"><a name="header.boost.utility.identity_type_hpp"></a>Header <<a href="../../../../../boost/utility/identity_type.hpp" target="_top">boost/utility/identity_type.hpp</a>></h3></div></div></div><p>Wrap type expressions with round parenthesis so they can be passed to macros even if they contain commas. </p><pre class="synopsis">
|
||||
|
||||
<a class="link" href="#BOOST_IDENTITY_TYPE" title="Macro BOOST_IDENTITY_TYPE">BOOST_IDENTITY_TYPE</a>(parenthesized_type)</pre><div class="refentry" title="Macro BOOST_IDENTITY_TYPE"><a name="BOOST_IDENTITY_TYPE"></a><div class="titlepage"></div><div class="refnamediv"><h2><span class="refentrytitle">Macro BOOST_IDENTITY_TYPE</span></h2><p>BOOST_IDENTITY_TYPE — This macro allows to wrap the specified type expression within extra round parenthesis so the type can be passed as a single macro parameter even if it contains commas (not already wrapped within round parenthesis). </p></div><h2 class="refsynopsisdiv-title">Synopsis</h2><div class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: <<a class="link" href="#header.boost.utility.identity_type_hpp" title="Header <boost/utility/identity_type.hpp>">boost/utility/identity_type.hpp</a>>
|
||||
|
||||
</span>BOOST_IDENTITY_TYPE(parenthesized_type)</pre></div><div class="refsect1" title="Description"><a name="id512092"></a><h2>Description</h2><p><span class="bold"><strong>Parameters:</strong></span> </p><div class="informaltable"><table class="table"><colgroup><col><col></colgroup><tbody><tr><td><span class="bold"><strong><code class="computeroutput">parenthesized_type</code></strong></span></td><td>The type expression to be passed as macro parameter wrapped by a single set of round parenthesis <code class="computeroutput">(...)</code>. This type expression can contain an arbitrary number of commas. </td></tr></tbody></table></div><p>
|
||||
</p><p>This macro works on any C++03 compiler (it does not require variadic macros).</p><p>This macro must be prefixed by <code class="computeroutput">typename</code> when used within templates. However, the compiler will not be able to automatically determine function template parameters when they are wrapped with this macro (these parameters need to be explicitly specified when calling the function template).</p><p>On some compilers (like GCC), using this macro on an abstract types requires to add and remove a reference to the type. </p></div></div></div></div><div class="footnotes"><br><hr width="100" align="left"><div class="footnote"><p><sup>[<a id="ftn.boost_utility_identitytype.solution.f0" href="#boost_utility_identitytype.solution.f0" class="para">1</a>] </sup>
|
||||
Using variadic macros, it would be possible to require a single set of extra
|
||||
parenthesis <code class="computeroutput"><span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">(</span></code><code class="literal"><span class="emphasis"><em>type</em></span></code><code class="computeroutput"><span class="special">)</span></code> instead of two <code class="computeroutput"><span class="identifier">BOOST_IDENTITY_TYPE</span><span class="special">((</span></code><code class="literal"><span class="emphasis"><em>type</em></span></code><code class="computeroutput"><span class="special">))</span></code> but variadic macros are not part of C++03
|
||||
(even if nowadays they are supported by most modern compilers and they are
|
||||
also part of C++11).
|
||||
</p></div><div class="footnote"><p><sup>[<a id="ftn.boost_utility_identitytype.templates.f0" href="#boost_utility_identitytype.templates.f0" class="para">2</a>] </sup>
|
||||
This is because the implementation of <code class="computeroutput"><a class="link" href="#BOOST_IDENTITY_TYPE" title="Macro BOOST_IDENTITY_TYPE">BOOST_IDENTITY_TYPE</a></code>
|
||||
wraps the specified type within a meta-function.
|
||||
</p></div><div class="footnote"><p><sup>[<a id="ftn.boost_utility_identitytype.annex__implementation.f0" href="#boost_utility_identitytype.annex__implementation.f0" class="para">3</a>] </sup>
|
||||
There is absolutely no guarantee that the macro is actually implemented using
|
||||
the code listed in this documentation. This code is for explanatory purposes
|
||||
only.
|
||||
</p></div></div></div></body></html>
|
||||
162
identity_type/doc/identity_type.qbk
Normal file
162
identity_type/doc/identity_type.qbk
Normal file
@ -0,0 +1,162 @@
|
||||
|
||||
[/ Copyright (C) 2009-2012 Lorenzo Caminiti ]
|
||||
[/ Distributed under the Boost Software License, Version 1.0 ]
|
||||
[/ (see accompanying file LICENSE_1_0.txt or a copy at ]
|
||||
[/ http://www.boost.org/LICENSE_1_0.txt) ]
|
||||
[/ Home at http://www.boost.org/libs/utility/identity_type ]
|
||||
|
||||
[library Boost.Utility/IdentityType
|
||||
[quickbook 1.5]
|
||||
[version 1.0.0]
|
||||
[copyright 2009-2012 Lorenzo Caminiti]
|
||||
[purpose wraps types with round parenthesis]
|
||||
[license
|
||||
Distributed under the Boost Software License, Version 1.0
|
||||
(see accompanying file LICENSE_1_0.txt or a copy at
|
||||
[@http://www.boost.org/LICENSE_1_0.txt])
|
||||
]
|
||||
[authors [Caminiti <email>lorcaminiti@gmail.com</email>, Lorenzo]]
|
||||
[category Utilities]
|
||||
]
|
||||
|
||||
This library allows to wrap type expressions within round parenthesis so they can be passed to macros even when they contain commas.
|
||||
|
||||
[import ../test/var_error.cpp]
|
||||
[import ../test/var.cpp]
|
||||
[import ../test/template.cpp]
|
||||
[import ../test/tmp_assert.cpp]
|
||||
|
||||
[section Motivation]
|
||||
|
||||
Consider the following macro which declares a variable named `var`[^['n]] with the specified [^['type]] (see also [@../../test/var_error.cpp =var_error.cpp=]):
|
||||
|
||||
[var_error]
|
||||
|
||||
The first macro invocation works correctly declaring a variable named `var1` of type `int`.
|
||||
However, the second macro invocation fails generating a preprocessor error similar to the following:
|
||||
|
||||
[pre
|
||||
error: macro "VAR" passed 3 arguments, but takes just 2
|
||||
]
|
||||
|
||||
That is because the `std::map` type passed as the first macro parameter contains a comma `,` not wrapped by round parenthesis `()`.
|
||||
The preprocessor interprets that unwrapped comma as a separation between macro parameters concluding that a total of three (and not two) parameters are passed to the macro in the following order:
|
||||
|
||||
# `std::map<int`
|
||||
# `char>`
|
||||
# `2`
|
||||
|
||||
Note that, differently from the compiler, the preprocessor only recognizes round parameters `()`.
|
||||
Angular `<>` or squared `[]` parenthesis are not used by the preprocessor when parsing the macro parameters.
|
||||
|
||||
[endsect]
|
||||
|
||||
[section Solution]
|
||||
|
||||
In some cases, it might be possible to workaround this issue by avoiding to pass the type expression to the macro all together.
|
||||
For example, in some cases a `typedef` can be used to specify the type expression with the commas outside the macro (see also [@../../test/var.cpp =var.cpp=]):
|
||||
|
||||
[var_typedef]
|
||||
|
||||
When this is not possible or desired (e.g., see the function template `f` in the section below), the library header [headerref boost/utility/identity_type.hpp] defines a macro [macroref BOOST_IDENTITY_TYPE] which can be used to workaround the issue while keeping the type expression as one of the macro parameters (see also [@../../test/var.cpp =var.cpp=]).
|
||||
|
||||
[var_ok]
|
||||
|
||||
This macro expands to an expression that evaluates (at compile-time) to the specified type.
|
||||
The specified type is never split into multiple macro parameters because it is always wrapped by a set of extra round parenthesis `()`.
|
||||
In fact, a total of two sets of round parenthesis must be used: The parenthesis to invoke the macro `BOOST_IDENTITY_TYPE(...)` plus the inner parenthesis to wrap the type passed to the macro `BOOST_IDENTITY_TYPE((...))`.
|
||||
|
||||
This macro works on any [@http://www.open-std.org/JTC1/SC22/WG21/docs/standards C++03] compiler (because it does not use [@http://en.wikipedia.org/wiki/Variadic_macro variadic macros]).
|
||||
[footnote
|
||||
Using variadic macros, it would be possible to require a single set of extra parenthesis `BOOST_IDENTITY_TYPE(`[^['type]]`)` instead of two `BOOST_IDENTITY_TYPE((`[^['type]]`))` but variadic macros are not part of C++03 (even if nowadays they are supported by most modern compilers and they are also part of C++11).
|
||||
]
|
||||
|
||||
[endsect]
|
||||
|
||||
[section Templates]
|
||||
|
||||
This macro must be prefixed by `typename` when used within templates.
|
||||
For example, let's program a macro that declares a function parameter named `arg`[^['n]] with the specified [^['type]] (see also [@../../test/template.cpp =template.cpp=]):
|
||||
|
||||
[template_f_decl]
|
||||
[template_f_call]
|
||||
|
||||
However, note that the template parameter `char` must be manually specified when invoking the function `f<char>(a)`.
|
||||
In fact, when the [macroref BOOST_IDENTITY_TYPE] macro is used to wrap a function template parameter, the template parameter can no longer be automatically deduced by the compiler form the function call as in `f(a)`.
|
||||
[footnote
|
||||
This is because the implementation of [macroref BOOST_IDENTITY_TYPE] wraps the specified type within a meta-function.
|
||||
]
|
||||
(This limitation does not apply to class templates because class template parameters must always be explicitly specified.)
|
||||
In other words, without using the [macroref BOOST_IDENTITY_TYPE] macro, C++ would normally be able to automatically deduce the function template parameter as shown below:
|
||||
|
||||
[template_g_decl]
|
||||
[template_g_call]
|
||||
|
||||
[endsect]
|
||||
|
||||
[section Abstract Types]
|
||||
|
||||
On some compilers (e.g., GCC), using this macro on abstract types (i.e., classes with one or more pure virtual functions) generates a compiler error.
|
||||
This can be worked around by manipulating the type adding and removing a reference to it.
|
||||
|
||||
Let's program a macro that performs a static assertion on a [@http://en.wikipedia.org/wiki/Template_metaprogramming Template Meta-Programming] (TMP) meta-function (similarly to Boost.MPL [@http://www.boost.org/doc/libs/1_36_0/libs/mpl/doc/refmanual/assert.html `BOOST_MPL_ASSERT`]).
|
||||
The [macroref BOOST_IDENTITY_TYPE] macro can be used to pass a meta-function with multiple template parameters to the assert macro (so to handle the commas separating the template parameters).
|
||||
In this case, if the meta-function is an abstract type, it needs to be manipulated adding and removing a reference to it (see also [@../../test/tmp_assert.cpp =tmp_assert.cpp=]):
|
||||
|
||||
[tmp_assert_abstract]
|
||||
|
||||
[endsect]
|
||||
|
||||
[section Annex: Usage]
|
||||
|
||||
The [macroref BOOST_IDENTITY_TYPE] macro can be used either when calling a user-defined macro (as shown by the examples so far), or internally in the definition of a user-defined macro (as shown below).
|
||||
When [macroref BOOST_IDENTITY_TYPE] is used in the user macro definition, the call of the user macro will only have to specify the extra parenthesis (see also [@../../test/tmp_assert.cpp =tmp_assert.cpp=]):
|
||||
|
||||
[tmp_assert_alternative]
|
||||
|
||||
However, note that the user will /always/ have to specify the extra parenthesis even when the macro parameters contain no comma:
|
||||
|
||||
[tmp_assert_alternative_always]
|
||||
|
||||
In some cases, using [macroref BOOST_IDENTITY_TYPE] within the user macro definition might provide the best syntax for the user.
|
||||
For example, this is the case for `BOOST_MPL_ASSERT` because the majority of template meta-programming expressions contain unwrapped commas so it is less confusing for the user to always specify the extra parenthesis `((...))` instead of using [macroref BOOST_IDENTITY_TYPE]:
|
||||
|
||||
BOOST_MPL_ASSERT(( // Natural syntax.
|
||||
boost::mpl::and_<
|
||||
boost::is_const<T>
|
||||
, boost::is_reference<T>
|
||||
>
|
||||
));
|
||||
|
||||
However, in other situations it might be preferable to not require the extra parenthesis in the common cases and handle commas as special cases using [macroref BOOST_IDENTITY_TYPE].
|
||||
For example, this is the case for [@http://www.boost.org/libs/local_function `BOOST_LOCAL_FUNCTION`] for which always requiring the extra parenthesis `((...))` around the types would lead to an unnatural syntax for the local function signature:
|
||||
|
||||
int BOOST_LOCAL_FUNCTION( ((int&)) x, ((int&)) y ) { // Unnatural syntax.
|
||||
return x + y;
|
||||
} BOOST_LOCAL_FUNCTION_NAME(add)
|
||||
|
||||
Instead requiring the user to specify [macroref BOOST_IDENTITY_TYPE] only when needed allows for the more natural syntax `BOOST_LOCAL_FUNCTION(int& x, int& y)` in the common cases when the parameter types contain no comma.
|
||||
|
||||
[endsect]
|
||||
|
||||
[section Annex: Implementation]
|
||||
|
||||
The implementation of this library macro is equivalent to the following:
|
||||
[footnote
|
||||
There is absolutely no guarantee that the macro is actually implemented using the code listed in this documentation.
|
||||
This code is for explanatory purposes only.
|
||||
]
|
||||
|
||||
#include <boost/type_traits/function_traits.hpp>
|
||||
|
||||
#define BOOST_IDENTITY_TYPE(parenthesized_type) \
|
||||
boost::function_traits<void parenthesized_type>::arg1_type
|
||||
|
||||
Essentially, the type is wrapped between round parenthesis `(std::map<int, char>)` so it can be passed as a single macro parameter even if it contains commas.
|
||||
Then the parenthesized type is transformed into the type of a function returning `void` and with the specified type as the type of the first and only argument `void (std::map<int, char>)`.
|
||||
Finally, the type of the first argument `arg1_type` is extracted at compile-time using the `function_traits` meta-function therefore obtaining the original type from the parenthesized type (effectively stripping the extra parenthesis from around the specified type).
|
||||
|
||||
[endsect]
|
||||
|
||||
[xinclude reference.xml]
|
||||
|
||||
15
identity_type/index.html
Normal file
15
identity_type/index.html
Normal file
@ -0,0 +1,15 @@
|
||||
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
||||
<html>
|
||||
<head>
|
||||
<meta http-equiv="refresh" content="0; URL=doc/html/index.html">
|
||||
</head>
|
||||
<body>
|
||||
Automatic redirection failed, click this
|
||||
<a href="doc/html/index.html">link</a> <hr>
|
||||
<p>© Copyright Lorenzo Caminiti, 2009-2012</p>
|
||||
<p>Distributed under the Boost Software License, Version 1.0 (see
|
||||
accompanying file <a href="../../../LICENSE_1_0.txt">
|
||||
LICENSE_1_0.txt</a> or a copy at
|
||||
<a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</p>
|
||||
</body>
|
||||
</html>
|
||||
14
identity_type/test/Jamfile.v2
Normal file
14
identity_type/test/Jamfile.v2
Normal file
@ -0,0 +1,14 @@
|
||||
|
||||
# Copyright (C) 2009-2012 Lorenzo Caminiti
|
||||
# Distributed under the Boost Software License, Version 1.0
|
||||
# (see accompanying file LICENSE_1_0.txt or a copy at
|
||||
# http://www.boost.org/LICENSE_1_0.txt)
|
||||
# Home at http://www.boost.org/libs/utility/identity_type
|
||||
|
||||
import testing ;
|
||||
|
||||
compile-fail var_error.cpp ;
|
||||
run var.cpp ;
|
||||
run template.cpp ;
|
||||
run tmp_assert.cpp ;
|
||||
|
||||
48
identity_type/test/template.cpp
Normal file
48
identity_type/test/template.cpp
Normal file
@ -0,0 +1,48 @@
|
||||
|
||||
// Copyright (C) 2009-2012 Lorenzo Caminiti
|
||||
// Distributed under the Boost Software License, Version 1.0
|
||||
// (see accompanying file LICENSE_1_0.txt or a copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt)
|
||||
// Home at http://www.boost.org/libs/utility/identity_type
|
||||
|
||||
#include <boost/utility/identity_type.hpp>
|
||||
#include <map>
|
||||
#include <iostream>
|
||||
|
||||
//[template_f_decl
|
||||
#define ARG(type, n) type arg ## n
|
||||
|
||||
template<typename T>
|
||||
void f( // Prefix macro with `typename` in templates.
|
||||
ARG(typename BOOST_IDENTITY_TYPE((std::map<int, T>)), 1)
|
||||
) {
|
||||
std::cout << arg1[0] << std::endl;
|
||||
}
|
||||
//]
|
||||
|
||||
//[template_g_decl
|
||||
template<typename T>
|
||||
void g(
|
||||
std::map<int, T> arg1
|
||||
) {
|
||||
std::cout << arg1[0] << std::endl;
|
||||
}
|
||||
//]
|
||||
|
||||
int main() {
|
||||
//[template_f_call
|
||||
std::map<int, char> a;
|
||||
a[0] = 'a';
|
||||
|
||||
f<char>(a); // OK...
|
||||
// f(a); // ... but error.
|
||||
//]
|
||||
|
||||
//[template_g_call
|
||||
g<char>(a); // OK...
|
||||
g(a); // ... and also OK.
|
||||
//]
|
||||
|
||||
return 0;
|
||||
}
|
||||
|
||||
53
identity_type/test/tmp_assert.cpp
Normal file
53
identity_type/test/tmp_assert.cpp
Normal file
@ -0,0 +1,53 @@
|
||||
|
||||
// Copyright (C) 2009-2012 Lorenzo Caminiti
|
||||
// Distributed under the Boost Software License, Version 1.0
|
||||
// (see accompanying file LICENSE_1_0.txt or a copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt)
|
||||
// Home at http://www.boost.org/libs/utility/identity_type
|
||||
|
||||
#include <boost/utility/identity_type.hpp>
|
||||
#include <boost/static_assert.hpp>
|
||||
#include <boost/type_traits/is_const.hpp>
|
||||
#include <boost/type_traits/add_reference.hpp>
|
||||
#include <boost/type_traits/remove_reference.hpp>
|
||||
#include <map>
|
||||
|
||||
//[tmp_assert_abstract
|
||||
#define TMP_ASSERT(metafunction) \
|
||||
BOOST_STATIC_ASSERT(metafunction::value)
|
||||
|
||||
template<typename T, bool b>
|
||||
struct abstract {
|
||||
static const bool value = b;
|
||||
virtual void f(T const& x) = 0; // Pure virtual function.
|
||||
};
|
||||
|
||||
TMP_ASSERT(
|
||||
boost::remove_reference< // Add and remove
|
||||
BOOST_IDENTITY_TYPE(( // reference for
|
||||
boost::add_reference< // abstract type.
|
||||
abstract<int, true>
|
||||
>::type
|
||||
))
|
||||
>::type
|
||||
);
|
||||
//]
|
||||
|
||||
//[tmp_assert_alternative
|
||||
#define TMP_ASSERT_PAREN(parenthesized_metafunction) \
|
||||
/* use `BOOST_IDENTITY_TYPE` in macro definition instead of invocation */ \
|
||||
BOOST_STATIC_ASSERT(BOOST_IDENTITY_TYPE(parenthesized_metafunction)::value)
|
||||
|
||||
// Specify only extra parenthesis `((...))`.
|
||||
TMP_ASSERT_PAREN((boost::is_const<std::map<int, char> const>));
|
||||
// Specify both the extra parenthesis `((...))` and `BOOST_IDENTITY_TYPE` macro.
|
||||
TMP_ASSERT(BOOST_IDENTITY_TYPE((boost::is_const<std::map<int, char> const>)));
|
||||
//]
|
||||
|
||||
//[tmp_assert_alternative_always
|
||||
TMP_ASSERT_PAREN((boost::is_const<int const>)); // Always extra `((...))`.
|
||||
TMP_ASSERT(boost::is_const<int const>); // No extra `((...))` and no macro.
|
||||
//]
|
||||
|
||||
int main() { return 0; }
|
||||
|
||||
26
identity_type/test/var.cpp
Normal file
26
identity_type/test/var.cpp
Normal file
@ -0,0 +1,26 @@
|
||||
|
||||
// Copyright (C) 2009-2012 Lorenzo Caminiti
|
||||
// Distributed under the Boost Software License, Version 1.0
|
||||
// (see accompanying file LICENSE_1_0.txt or a copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt)
|
||||
// Home at http://www.boost.org/libs/utility/identity_type
|
||||
|
||||
#include <map>
|
||||
|
||||
#define VAR(type, n) type var ## n
|
||||
|
||||
VAR(int, 1); // OK.
|
||||
|
||||
//[var_typedef
|
||||
typedef std::map<int, char> map_type;
|
||||
VAR(map_type, 3); // OK.
|
||||
//]
|
||||
|
||||
//[var_ok
|
||||
#include <boost/utility/identity_type.hpp>
|
||||
|
||||
VAR(BOOST_IDENTITY_TYPE((std::map<int, char>)), 4); // OK.
|
||||
//]
|
||||
|
||||
int main() { return 0; }
|
||||
|
||||
18
identity_type/test/var_error.cpp
Normal file
18
identity_type/test/var_error.cpp
Normal file
@ -0,0 +1,18 @@
|
||||
|
||||
// Copyright (C) 2009-2012 Lorenzo Caminiti
|
||||
// Distributed under the Boost Software License, Version 1.0
|
||||
// (see accompanying file LICENSE_1_0.txt or a copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt)
|
||||
// Home at http://www.boost.org/libs/utility/identity_type
|
||||
|
||||
#include <map>
|
||||
|
||||
//[var_error
|
||||
#define VAR(type, n) type var ## n
|
||||
|
||||
VAR(int, 1); // OK.
|
||||
VAR(std::map<int, char>, 2); // Error.
|
||||
//]
|
||||
|
||||
int main() { return 0; }
|
||||
|
||||
@ -1,6 +1,6 @@
|
||||
// boost utility/base_from_member.hpp header file --------------------------//
|
||||
|
||||
// Copyright 2001, 2003, 2004 Daryle Walker. Use, modification, and
|
||||
// Copyright 2001, 2003, 2004, 2012 Daryle Walker. Use, modification, and
|
||||
// distribution are subject to the Boost Software License, Version 1.0. (See
|
||||
// accompanying file LICENSE_1_0.txt or a copy at
|
||||
// <http://www.boost.org/LICENSE_1_0.txt>.)
|
||||
@ -10,10 +10,15 @@
|
||||
#ifndef BOOST_UTILITY_BASE_FROM_MEMBER_HPP
|
||||
#define BOOST_UTILITY_BASE_FROM_MEMBER_HPP
|
||||
|
||||
#include <boost/config.hpp>
|
||||
#include <boost/preprocessor/arithmetic/inc.hpp>
|
||||
#include <boost/preprocessor/repetition/enum_binary_params.hpp>
|
||||
#include <boost/preprocessor/repetition/enum_params.hpp>
|
||||
#include <boost/preprocessor/repetition/repeat_from_to.hpp>
|
||||
#include <boost/type_traits/is_same.hpp>
|
||||
#include <boost/type_traits/remove_cv.hpp>
|
||||
#include <boost/type_traits/remove_reference.hpp>
|
||||
#include <boost/utility/enable_if.hpp>
|
||||
|
||||
|
||||
// Base-from-member arity configuration macro ------------------------------//
|
||||
@ -53,6 +58,59 @@
|
||||
namespace boost
|
||||
{
|
||||
|
||||
namespace detail
|
||||
{
|
||||
|
||||
// Type-unmarking class template -------------------------------------------//
|
||||
|
||||
// Type-trait to get the raw type, i.e. the type without top-level reference nor
|
||||
// cv-qualification, from a type expression. Mainly for function arguments, any
|
||||
// reference part is stripped first.
|
||||
|
||||
// Contributed by Daryle Walker
|
||||
|
||||
template < typename T >
|
||||
struct remove_cv_ref
|
||||
{
|
||||
typedef typename ::boost::remove_cv<typename
|
||||
::boost::remove_reference<T>::type>::type type;
|
||||
|
||||
}; // boost::detail::remove_cv_ref
|
||||
|
||||
// Unmarked-type comparison class template ---------------------------------//
|
||||
|
||||
// Type-trait to check if two type expressions have the same raw type.
|
||||
|
||||
// Contributed by Daryle Walker, based on a work-around by Luc Danton
|
||||
|
||||
template < typename T, typename U >
|
||||
struct is_related
|
||||
: public ::boost::is_same<
|
||||
typename ::boost::detail::remove_cv_ref<T>::type,
|
||||
typename ::boost::detail::remove_cv_ref<U>::type >
|
||||
{};
|
||||
|
||||
// Enable-if-on-unidentical-unmarked-type class template -------------------//
|
||||
|
||||
// Enable-if on the first two type expressions NOT having the same raw type.
|
||||
|
||||
// Contributed by Daryle Walker, based on a work-around by Luc Danton
|
||||
|
||||
#ifndef BOOST_NO_VARIADIC_TEMPLATES
|
||||
template<typename ...T>
|
||||
struct enable_if_unrelated
|
||||
: public ::boost::enable_if_c<true>
|
||||
{};
|
||||
|
||||
template<typename T, typename U, typename ...U2>
|
||||
struct enable_if_unrelated<T, U, U2...>
|
||||
: public ::boost::disable_if< ::boost::detail::is_related<T, U> >
|
||||
{};
|
||||
#endif
|
||||
|
||||
} // namespace boost::detail
|
||||
|
||||
|
||||
// Base-from-member class template -----------------------------------------//
|
||||
|
||||
// Helper to initialize a base object so a derived class can use this
|
||||
@ -68,12 +126,24 @@ class base_from_member
|
||||
protected:
|
||||
MemberType member;
|
||||
|
||||
#if !defined(BOOST_NO_RVALUE_REFERENCES) && \
|
||||
!defined(BOOST_NO_VARIADIC_TEMPLATES) && \
|
||||
!defined(BOOST_NO_FUNCTION_TEMPLATE_DEFAULT_ARGS)
|
||||
template <typename ...T, typename EnableIf = typename
|
||||
::boost::detail::enable_if_unrelated<base_from_member, T...>::type>
|
||||
explicit BOOST_CONSTEXPR base_from_member( T&& ...x )
|
||||
BOOST_NOEXCEPT_IF( BOOST_NOEXCEPT_EXPR(::new ((void*) 0) MemberType(
|
||||
static_cast<T&&>(x)... )) ) // no std::is_nothrow_constructible...
|
||||
: member( static_cast<T&&>(x)... ) // ...nor std::forward needed
|
||||
{}
|
||||
#else
|
||||
base_from_member()
|
||||
: member()
|
||||
{}
|
||||
|
||||
BOOST_PP_REPEAT_FROM_TO( 1, BOOST_PP_INC(BOOST_BASE_FROM_MEMBER_MAX_ARITY),
|
||||
BOOST_PRIVATE_CTR_DEF, _ )
|
||||
#endif
|
||||
|
||||
}; // boost::base_from_member
|
||||
|
||||
|
||||
45
include/boost/utility/identity_type.hpp
Normal file
45
include/boost/utility/identity_type.hpp
Normal file
@ -0,0 +1,45 @@
|
||||
|
||||
// Copyright (C) 2009-2012 Lorenzo Caminiti
|
||||
// Distributed under the Boost Software License, Version 1.0
|
||||
// (see accompanying file LICENSE_1_0.txt or a copy at
|
||||
// http://www.boost.org/LICENSE_1_0.txt)
|
||||
// Home at http://www.boost.org/libs/utility/identity_type
|
||||
|
||||
/** @file
|
||||
Wrap type expressions with round parenthesis so they can be passed to macros
|
||||
even if they contain commas.
|
||||
*/
|
||||
|
||||
#ifndef BOOST_IDENTITY_TYPE_HPP_
|
||||
#define BOOST_IDENTITY_TYPE_HPP_
|
||||
|
||||
#include <boost/type_traits/function_traits.hpp>
|
||||
|
||||
/**
|
||||
@brief This macro allows to wrap the specified type expression within extra
|
||||
round parenthesis so the type can be passed as a single macro parameter even if
|
||||
it contains commas (not already wrapped within round parenthesis).
|
||||
|
||||
@Params
|
||||
@Param{parenthesized_type,
|
||||
The type expression to be passed as macro parameter wrapped by a single set
|
||||
of round parenthesis <c>(...)</c>.
|
||||
This type expression can contain an arbitrary number of commas.
|
||||
}
|
||||
@EndParams
|
||||
|
||||
This macro works on any C++03 compiler (it does not require variadic macros).
|
||||
|
||||
This macro must be prefixed by <c>typename</c> when used within templates.
|
||||
However, the compiler will not be able to automatically determine function template parameters when they are wrapped with this macro (these parameters need to
|
||||
be explicitly specified when calling the function template).
|
||||
|
||||
On some compilers (like GCC), using this macro on an abstract types requires to
|
||||
add and remove a reference to the type.
|
||||
*/
|
||||
#define BOOST_IDENTITY_TYPE(parenthesized_type) \
|
||||
/* must NOT prefix this with `::` to work with parenthesized syntax */ \
|
||||
boost::function_traits< void parenthesized_type >::arg1_type
|
||||
|
||||
#endif // #include guard
|
||||
|
||||
Loading…
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Reference in New Issue
Block a user