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Minor "beautifications" of value_init documentation, inc. placing references in order of appearance

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[SVN r42779]
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Niels Dekker 2008-01-14 21:46:20 +00:00
parent ac93de7c1b
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1 changed files with 13 additions and 13 deletions
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value_init.htm
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@ -32,7 +32,7 @@
</dl>
<ul>
<li><a href="#val_init"><code>value_initialized&lt;&gt;</code></a></li>
<li><a href="#val_init"><code>value_initialized&lt;T&gt;</code></a></li>
</ul>
<a href="#acknowledgements">Acknowledgements</a><br>
@ -46,7 +46,7 @@
for initialization. Depending on the type, the value of a newly constructed
object can be zero-initialized (logically 0), default-constructed (using
the default constructor), or indeterminate. When writing generic code,
this problem must be addressed. <code>value_initialized</code> provides
this problem must be addressed. The template <code>value_initialized</code> provides
a solution with consistent syntax for value initialization of scalar,
union and class types.
Moreover, <code>value_initialized</code> offers a workaround to various
@ -84,7 +84,7 @@ initialized that way). The third form, <code>T3 var3 = {}</code>
initializes an aggregate, typically a "C-style" <code>struct</code> or a "C-style" array.
However, the syntax is not allowed for a class that has an explicitly declared
constructor. (But watch out for an upcoming C++ language change,
by Bjarne Stroustrup et al [<a href="#references">3</a>]!)
by Bjarne Stroustrup et al [<a href="#references">1</a>]!)
The fourth form is the most generic form of them, as it
can be used to initialize arithmetic types, class types, aggregates, pointers, and
other types. The declaration, <code>T4 var4 = T4()</code>, should be read
@ -98,7 +98,7 @@ be optimized away, C++ still requires the type <code>T4</code> to be
A class may not be CopyConstructible, for example because it may have a
private and undefined copy constructor,
or because it may be derived from <a href="utility.htm#Class_noncopyable">boost::noncopyable</a>.
Scott Meyers [<a href="#references">4</a>] explains why a class would be defined like that.
Scott Meyers [<a href="#references">2</a>] explains why a class would be defined like that.
</p>
<p>
There is another, less obvious disadvantage to the fourth form, <code>T4 var4 = T4()</code>:
@ -120,11 +120,11 @@ constructed by the following declaration:
</p>
<h2><a name="details"></a>Details</h2>
<p>The C++ standard [<a href="#references">1</a>] contains the definitions
<p>The C++ standard [<a href="#references">3</a>] contains the definitions
of <code>zero-initialization</code> and <code>default-initialization</code>.
Informally, zero-initialization means that the object is given the initial
value 0 (converted to the type) and default-initialization means that
POD [<a href="#references">2</a>] types are zero-initialized, while non-POD class
POD [<a href="#references">4</a>] types are zero-initialized, while non-POD class
types are initialized with their corresponding default constructors. A
<i>declaration</i> can contain an <i>initializer</i>, which specifies the
object's initial value. The initializer can be just '()', which states that
@ -225,7 +225,7 @@ GCC Bug 33916 - Default constructor fails to initialize array members</a>
<br>
<a href="http://qc.codegear.com/wc/qcmain.aspx?d=51854">
Borland Report 51854 - Value-initialization: POD struct should be zero-initialized</a>
<br>Reported by Niels Dekker (LKEB, Leiden University Medical Center), 2007-11-09
<br>Reported by Niels Dekker (LKEB, Leiden University Medical Center), 2007-09-11
<br>
</td></tr></table>
</p><p>
@ -299,23 +299,23 @@ the wrapped object is always performed with the <code>get()</code> idiom:</p>
<pre>value_initialized&lt;int&gt; x ;<br>get(x) = 1 ; // OK<br><br>value_initialized&lt;int const&gt; cx ;<br>get(x) = 1 ; // ERROR: Cannot modify a const object<br><br>value_initialized&lt;int&gt; const x_c ;<br>get(x_c) = 1 ; // ERROR: Cannot modify a const object<br><br>value_initialized&lt;int const&gt; const cx_c ;<br>get(cx_c) = 1 ; // ERROR: Cannot modify a const object<br></pre>
<h3><a name="references">References</a></h3>
[1] The C++ Standard, Second edition (2003), ISO/IEC 14882:2003 <br>
[2] POD stands for "Plain Old Data" <br>
[3] Bjarne Stroustrup, Gabriel Dos Reis, and J. Stephen Adamczyk wrote
[1] Bjarne Stroustrup, Gabriel Dos Reis, and J. Stephen Adamczyk wrote
various papers, proposing to extend the support for brace-enclosed <em>initializer lists</em>
in the next version of C++.
This would allow a variable <code>var</code> of any DefaultConstructible type
<code>T</code> to be <em>value-initialized</em> by doing <code>T var = {}</code>.
The papers are listed at Bjarne's web page,
<a href="http://www.research.att.com/~bs/WG21.html">My C++ Standards committee papers</a> <br>
[4] Scott Meyers, Effective C++, Third Edition, item 6,
[2] Scott Meyers, Effective C++, Third Edition, item 6,
<em>Explicitly disallow the use of compiler-generated functions you do not want</em>,
<a href="http://www.aristeia.com/books.html">Scott Meyers: Books and CDs</a>
<a href="http://www.aristeia.com/books.html">Scott Meyers: Books and CDs</a> <br>
[3] The C++ Standard, Second edition (2003), ISO/IEC 14882:2003 <br>
[4] POD stands for "Plain Old Data"
<h3><a name="acknowledgements"></a>Acknowledgements</h3>
value_initialized was developed by Fernando Cacciola, with help and
suggestions from David Abrahams and Darin Adler.<br>
Special thanks to Björn Karlsson who carefully edited and completed this documentation.
Special thanks to Bj&ouml;rn Karlsson who carefully edited and completed this documentation.
<p>value_initialized was reimplemented by Fernando Cacciola and Niels Dekker
for Boost release version 1.35 (2008), offering a workaround to various compiler issues.