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<h1 class="c1"><a href="../index.html">Boost.Python</a></h1>
<h2 class="c2">Header <boost/python/type_id.hpp></h2>
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<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a>
<dt><a href="#classes">Classes</a>
<dd>
<dl class="page-index">
<dt><a href="#type_info-spec">Class
<code>type_info</code></a>
<dd>
<dl class="page-index">
<dt><a href="#type_info-spec-synopsis">Class
<code>type_info</code> synopsis</a>
<dt><a href="#type_infospec-ctors">Class
<code>type_info</code> constructor</a>
<dt><a href="#type_infospec-comparisons">Class
<code>type_info</code> comparison functions</a>
<dt><a href="#type_infospec-observers">Class
<code>type_info</code> observer functions</a>
</dl>
</dl>
<dt><a href="#functions">Functions</a>
<dd>
<dl class="page-index">
<dt><a href="#type_id-spec">type_id</a>
</dl>
<dt><a href="#examples">Example</a>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code><boost/python/type_id.hpp></code> provides types and
functions for runtime type identification like those of of
<code><typeinfo></code>. It exists mostly to work around
certain compiler bugs and platform-dependent interactions with
shared libraries.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="type_info-spec"></a>Class <code>type_info</code></h3>
<p><code>type_info</code> instances identify a type. As
<code>std::type_info</code> is specified to (but unlike its
implementation in some compilers),
<code>boost::python::type_info</code> never represents top-level
references or cv-qualification (see section 5.2.8 in the C++
standard). Unlike <code>std::type_info</code>,
<code>boost::python::type_info</code> instances are copyable, and
comparisons always work reliably across shared library boundaries.
<h4><a name="type_info-spec-synopsis"></a>Class type_info
synopsis</h4>
<pre>
namespace boost { namespace python
{
class type_info : <a href=
"../../../utility/operators.htm#totally_ordered1">totally_ordered</a><type_info>
{
public:
// constructor
type_info(std::type_info const& = typeid(void));
// comparisons
bool operator<(type_info const& rhs) const;
bool operator==(type_info const& rhs) const;
// observers
char const* name() const;
};
}}
</pre>
<h4><a name="type_infospec-ctors">Class <code>type_info</code>
constructor</a></h4>
<pre>
type_info(std::type_info const& = typeid(void));
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> constructs a <code>type_info</code> object
which identifies the same type as its argument.
<dt><b>Rationale:</b> Since it is occasionally neccessary to make
an array of <code>type_info</code> objects a benign default
argument is supplied. <span class="c3"><b>Note:</b></span> this
constructor does <i>not</i> correct for non-conformance of
compiler <code>typeid()</code> implementations. See <code><a
href="#type_id-spec">type_id</a></code>, below.
</dl>
<h4><a name="type_infospec-comparisons">Class
<code>type_info</code> comparisons</a></h4>
<pre>
bool operator<(type_info const& rhs) const;
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> yields a total order over
<code>type_info</code> objects.
</dl>
<pre>
bool operator==(type_info const& rhs) const;
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>true</code> iff the two values describe
the same type.
</dl>
<dl class="function-semantics">
<dt><b>Note:</b> The use of <code><a href=
"../../../utility/operators.htm#totally_ordered1">totally_ordered</a><type_info></code>
as a private base class supplies operators <code><=</code>,
<code>>=</code>, <code>></code>, and <code>!=</code>
</dl>
<h4><a name="type_infospec-observers">Class <code>type_info</code>
observers</a></h4>
<pre>
char const* name() const;
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> The result of calling <code>name()</code> on
the argument used to construct the object.
</dl>
<h2><a name="functions"></a>Functions</h2>
<pre>
std::ostream& operator<<(std::ostream&s, type_info const&x);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> Writes a description of the type described by
to <code>x</code> into <code>s</code>.
<dt><b>Rationale:</b> Not every C++ implementation provides a
truly human-readable <code>type_info::name()</code> string, but
for some we may be able to decode the string and produce a
reasonable representation.
</dl>
<pre>
<a name="type_id-spec">template <class T> type_info type_id</a>()
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>type_info(typeid(T))</code>
<dt><b>Note:</b> On some non-conforming C++ implementations, the
code is not actually as simple as described above; the semantics
are adjusted to work <i>as-if</i> the C++ implementation were
conforming.
</dl>
<h2><a name="examples"></a>Example</h2>
The following example, though silly, illustrates how the
<code>type_id</code> facility might be used
<pre>
#include <boost/python/type_id.hpp>
// Returns true iff the user passes an int argument
template <class T>
bool is_int(T x)
{
using boost::python::type_id;
return type_id<T>() == type_id<int>();
}
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
13 November, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p class="c4">© Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All
Rights Reserved.
