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Updated boost::base_from_member for C++2011.

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[SVN r76982]
This commit is contained in:
Daryle Walker 2012-02-11 18:27:02 +00:00
parent fe653d0a9a
commit e763315b55
2 changed files with 49 additions and 14 deletions
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51
base_from_member.html
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@ -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>
#include &lt;type_traits&gt; <i>// exposition only</i>
#ifndef BOOST_BASE_FROM_MEMBER_MAX_ARITY
#define BOOST_BASE_FROM_MEMBER_MAX_ARITY 10
#endif
@ -139,6 +141,11 @@ class boost::base_from_member
protected:
MemberType member;
#if <i>C++2011 is in use</i>
template&lt; typename ...T &gt;
explicit constexpr base_from_member( T&amp;&amp; ...x )
noexcept( std::is_nothrow_constructible&lt;MemberType, T...&gt;::value );
#else
base_from_member();
template&lt; typename T1 &gt;
@ -154,6 +161,7 @@ protected:
typename T10 &gt;
base_from_member( T1 x1, T2 x2, T3 x3, T4 x4, T5 x5, T6 x6, T7 x7,
T8 x8, T9 x9, T10 x10 );
#endif
};
</pre></blockquote>
@ -166,13 +174,27 @@ value of zero if it is omitted. The class template has a protected
data member called <var>member</var> that the derived class can use
for later base classes (or itself).</p>
<p>There is a default constructor and several constructor member
templates. These constructor templates can take as many arguments
(currently up to ten) as possible and pass them to a constructor of
the data member. Since C++ does not allow any way to explicitly state
<p>If the variadic template arguments and r-value reference features of C++2011
are present, there will be a single constructor template. It implements
&quot;perfect forwarding&quot; to the best constructor call of
<code>member</code> (if any). The constructor template is marked both
<code>constexpr</code> and <code>explicit</code>. The former will be ignored
if the corresponding inner constructor call (of <code>member</code>) does not
have the marker. The latter binds the other way; always taking effect, even
when the inner constructor call does not have the marker. The constructor
template propagates the <code>noexcept</code> status of the inner constructor
call.</p>
<p>On earlier-standard compilers, there is a default constructor and several
constructor member templates. These constructor templates can take as many
arguments (currently up to ten) as possible and pass them to a constructor of
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
the arguments are already close as possible to the actual type used in
the data member's desired constructor.</p>
the data member's desired constructor. Explicit conversions may be
necessary.</p>
<p>The <var>BOOST_BASE_FROM_MEMBER_MAX_ARITY</var> macro constant specifies
the maximum argument length for the constructor templates. The constant
@ -180,7 +202,7 @@ may be overridden if more (or less) argument configurations are needed. The
constant may be read for code that is expandable like the class template and
needs to maintain the same maximum size. (Example code would be a class that
uses this class template as a base class for a member with a flexible set of
constructors.)</p>
constructors.) This constant is ignored when C++2011 features are present.</p>
<h2><a name="usage">Usage</a></h2>
@ -323,11 +345,14 @@ constructor argument for <code>pbase0_type</code> is converted from
argument for <code>pbase2_type</code> is converted from <code>int</code>
to <code>double</code>. The second constructor argument for
<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
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 +385,9 @@ with the exact pointer type used in <code>switcher</code>'s constructor.</p>
<hr>
<p>Revised: 28 August 2004</p>
<p>Revised: 11 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 &lt;<a
href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>&gt;.)</p>

12
include/boost/utility/base_from_member.hpp
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@ -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>.)
@ -10,6 +10,7 @@
#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>
@ -68,12 +69,21 @@ class base_from_member
protected:
MemberType member;
#if defined(BOOST_HAS_RVALUE_REFS) && defined(BOOST_HAS_VARIADIC_TMPL)
template <typename ...T>
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