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Add polymorphic_pointer_cast

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Antony Polukhin
2014-11-10 15:02:20 +04:00
parent 6199649ae2
commit 00b6a53f7e
3 changed files with 113 additions and 11 deletions
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cast.htm
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@@ -30,7 +30,8 @@
<code><a href="#Polymorphic_cast">polymorphic_cast</a></code> and
<code><a href="#Polymorphic_cast">polymorphic_downcast</a></code>
function templates designed to complement the C++ built-in casts.</p> <p>The header <a href="../../boost/polymorphic_pointer_cast.hpp">boost/polymorphic_pointer_cast.hpp</a> provides
<code><a href="#Polymorphic_cast">polymorphic_pointer_downcast</a></code> function template.
<code><a href="#Polymorphic_cast">polymorphic_pointer_cast</a></code> and
<code><a href="#Polymorphic_cast">polymorphic_pointer_downcast</a></code> function templates.
<p>The program <a href="test/cast_test.cpp">cast_test.cpp</a> can be used to
verify these function templates work as expected.</p>
@@ -79,7 +80,7 @@
<b>Warning:</b> Because <code>polymorphic_downcast</code> uses assert(), it
violates the One Definition Rule (ODR) if NDEBUG is inconsistently
defined across translation units. [See ISO Std 3.2]
</p><p>
<p>
For crosscasts, or when the success of a cast can only be known at
runtime, or when efficiency is not important,
<code>polymorphic_cast</code> is preferred. </p>
@@ -89,13 +90,18 @@
whether a given interface is supported; in that case a return of 0 isn't
an error condition.</p>
<p>While <code>polymorphic_downcast</code> works with built-in pointer types only,
<code>polymorphic_pointer_downcast</code> is a more generic version
<p>While <code>polymorphic_downcast</code> and <code>polymorphic_cast</code> work with built-in pointer types only,
<code>polymorphic_pointer_downcast</code> and <code>polymorphic_pointer_cast</code> are more generic versions
with support for any pointer type for which the following expressions would be valid:<br><br>
<code>&nbsp;&nbsp;static_pointer_cast&lt;Derived&gt;(p);<br>&nbsp;&nbsp;dynamic_pointer_cast&lt;Derived&gt;(p);</code><br><br>
This includes C++ built-in pointers, <code>std::shared_ptr, boost::shared_ptr, boost::intrusive_ptr</code>, etc.</p>
<h3>polymorphic_cast, polymorphic_downcast and polymorphic_pointer_downcast synopsis</h3>
<p> For <code>polymorphic_pointer_downcast</code>:</p>
<code>&nbsp;&nbsp;static_pointer_cast&lt;Derived&gt;(p);<br>&nbsp;&nbsp;dynamic_pointer_cast&lt;Derived&gt;(p);</code><br><br>
<p> For <code>polymorphic_pointer_cast</code>:</p>
<code>&nbsp;&nbsp;dynamic_pointer_cast&lt;Derived&gt;(p);<br>&nbsp;&nbsp;!p; // conversion to bool with negation</code><br><br>
<p>This includes C++ built-in pointers, <code>std::shared_ptr, boost::shared_ptr, boost::intrusive_ptr</code>, etc.</p>
<h3>polymorphic_cast, polymorphic_downcast, polymorphic_pointer_cast and polymorphic_pointer_downcast synopsis</h3>
<blockquote>
<pre>namespace boost {
@@ -110,6 +116,11 @@ inline Derived polymorphic_downcast(Base* x);
// Effects: assert( dynamic_cast&lt;Derived&gt;(x) == x );
// Returns: static_cast&lt;Derived&gt;(x)
template &lt;class Derived, class Base&gt;
inline Derived polymorphic_pointer_cast(Base* x);
// Throws: std::bad_cast if ( dynamic_pointer_cast&lt;Derived&gt;(x) == 0 )
// Returns: dynamic_pointer_cast&lt;Derived&gt;(x)
template &lt;class Derived, class Base&gt;
inline auto polymorphic_pointer_downcast(Base x);
// Effects: assert( dynamic_pointer_cast&lt;Derived&gt;(x) == x );
@@ -165,7 +176,8 @@ void f(FruitPtr fruit)
<code>polymorphic_downcast</code> was contributed by <a href=
"http://www.boost.org/people/dave_abrahams.htm">Dave Abrahams</a>.<br>
<code>polymorphic_pointer_downcast</code> was contributed by <a href=
"http://www.boost.org/people/boris_rasin.htm">Boris Rasin</a>.<br>
"http://www.boost.org/people/boris_rasin.htm">Boris Rasin</a> and
<code>polymorphic_pointer_cast</code> by Antony Polukhin.<br>
An old
<code>numeric_cast</code> that was contributed by <a href=
"http://www.boost.org/people/kevlin_henney.htm">Kevlin Henney</a> is now superseeded by the <a href="../numeric/conversion/doc/html/index.html">Boost Numeric Conversion Library</a></p>