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source: downloads/boost_1_34_1/libs/bind/mem_fn.html @ 33

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1	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
2	<html>
3	<head>
4	<title>Boost: mem_fn.hpp documentation</title>
5	<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
6	</head>
7	<body bgcolor="white" style="MARGIN-LEFT: 5%; MARGIN-RIGHT: 5%">
8	<table border="0" width="100%">
9	<tr>
10	<td width="277"><A href="../../index.htm"> <img src="../../boost.png" alt="boost.png (6897 bytes)" width="277" height="86" border="0"></A>
11	</td>
12	<td align="center">
13	<h1>mem_fn.hpp</h1>
14	</td>
15	</tr>
16	<tr>
17	<td colspan="2" height="64"> </td>
18	</tr>
19	</table>
20	<h2>Contents</h2>
21	<h3 style="MARGIN-LEFT: 20pt"><a href="#Purpose">Purpose</a></h3>
22	<h3 style="MARGIN-LEFT: 20pt"><a href="#FAQ">Frequently Asked Questions</a></h3>
23	<h4 style="MARGIN-LEFT: 40pt"><a href="#Q1">Can <b>mem_fn</b> be used instead of the
24	standard <b>std::mem_fun[_ref]</b> adaptors?</a></h4>
25	<h4 style="MARGIN-LEFT: 40pt"><a href="#Q2">Should I replace every occurence of <b>std::mem_fun[_ref]</b>
26	with <b>mem_fn</b> in my existing code?</a></h4>
27	<h4 style="MARGIN-LEFT: 40pt"><a href="#Q3">Does <b>mem_fn</b> work with COM methods?</a></h4>
28	<h4 style="MARGIN-LEFT: 40pt"><a href="#Q4">Why isn't BOOST_MEM_FN_ENABLE_STDCALL
29	defined automatically?</a></h4>
30	<h3 style="MARGIN-LEFT: 20pt"><a href="#Interface">Interface</a></h3>
31	<h4 style="MARGIN-LEFT: 40pt"><a href="#Synopsis">Synopsis</a></h4>
32	<h4 style="MARGIN-LEFT: 40pt"><a href="#CommonRequirements">Common requirements</a></h4>
33	<h4 style="MARGIN-LEFT: 40pt"><a href="#get_pointer">get_pointer</a></h4>
34	<h4 style="MARGIN-LEFT: 40pt"><a href="#mem_fn">mem_fn</a></h4>
35	<h3 style="MARGIN-LEFT: 20pt"><a href="#Implementation">Implementation</a></h3>
36	<h4 style="MARGIN-LEFT: 40pt"><a href="#Files">Files</a></h4>
37	<h4 style="MARGIN-LEFT: 40pt"><a href="#Dependencies">Dependencies</a></h4>
38	<h4 style="MARGIN-LEFT: 40pt"><a href="#NumberOfArguments">Number of Arguments</a></h4>
39	<h4 style="MARGIN-LEFT: 40pt"><a href="#stdcall">"__stdcall", "__cdecl" and
40	"__fastcall" Support</a></h4>
41	<h3 style="MARGIN-LEFT: 20pt"><a href="#Acknowledgements">Acknowledgements</a></h3>
42	<h2><a name="Purpose">Purpose</a></h2>
43	<p>
44	<b>boost::mem_fn</b> is a generalization of the standard functions <b>std::mem_fun</b>
45	and <b>std::mem_fun_ref</b>. It supports member function pointers with more
46	than one argument, and the returned function object can take a pointer, a
47	reference, or a smart pointer to an object instance as its first argument. <STRONG>mem_fn</STRONG>
48	also supports pointers to data members by treating them as functions taking no
49	arguments and returning a (const) reference to the member.
50	</p>
51	<p>
52	The purpose of <b>mem_fn</b> is twofold. First, it allows users to invoke a
53	member function on a container with the familiar
54	</p>
55	<pre>
56	std::for_each(v.begin(), v.end(), boost::mem_fn(&Shape::draw));
57	</pre>
58	<p>
59	syntax, even when the container stores smart pointers.
60	</p>
61	<p>
62	Second, it can be used as a building block by library developers that want to
63	treat a pointer to member function as a function object. A library might define
64	an enhanced <b>for_each</b> algorithm with an overload of the form:
65	</p>
66	<pre>
67	template<class It, class R, class T> void for_each(It first, It last, R (T::*pmf) ())
68	{
69	std::for_each(first, last, boost::mem_fn(pmf));
70	}
71	</pre>
72	<p>
73	that will allow the convenient syntax:
74	</p>
75	<pre>
76	for_each(v.begin(), v.end(), &Shape::draw);
77	</pre>
78	<p>
79	When documenting the feature, the library author will simply state:
80	</p>
81	<h4 style="MARGIN-LEFT: 20pt">template<class It, class R, class T> void
82	for_each(It first, It last, R (T::*pmf) ());</h4>
83	<p style="MARGIN-LEFT: 20pt">
84	<b>Effects:</b> equivalent to std::for_each(first, last, boost::mem_fn(pmf));
85	</p>
86	<p>
87	where <b>boost::mem_fn</b> can be a link to this page. See <a href="bind.html">the
88	documentation of <b>bind</b></a> for an example.
89	</p>
90	<p>
91	<b>mem_fn</b> takes one argument, a pointer to a member, and returns a function
92	object suitable for use with standard or user-defined algorithms:
93	</p>
94	<pre>
95	struct X
96	{
97	void f();
98	};
99
100	void g(std::vector<X> & v)
101	{
102	std::for_each(v.begin(), v.end(), boost::mem_fn(&X::f));
103	};
104
105	void h(std::vector<X *> const & v)
106	{
107	std::for_each(v.begin(), v.end(), boost::mem_fn(&X::f));
108	};
109
110	void k(std::vector<boost::shared_ptr<X> > const & v)
111	{
112	std::for_each(v.begin(), v.end(), boost::mem_fn(&X::f));
113	};
114	</pre>
115	<p>
116	The returned function object takes the same arguments as the input member
117	function plus a "flexible" first argument that represents the object instance.
118	</p>
119	<p>
120	When the function object is invoked with a first argument <b>x</b> that is
121	neither a pointer nor a reference to the appropriate class (<b>X</b> in the
122	example above), it uses <tt>get_pointer(x)</tt> to obtain a pointer from <b>x</b>.
123	Library authors can "register" their smart pointer classes by supplying an
124	appropriate <b>get_pointer</b> overload, allowing <b>mem_fn</b> to recognize
125	and support them.
126	</p>
127	<p>
128	[Note: <b>get_pointer</b> is not restricted to return a pointer. Any object
129	that can be used in a member function call expression <tt>(x->*pmf)(...)</tt>
130	will work.]
131	</p>
132	<p>
133	[Note: the library uses an unqualified call to <b>get_pointer</b>. Therefore,
134	it will find, through argument-dependent lookup, <b>get_pointer</b> overloads
135	that are defined in the same namespace as the corresponding smart pointer
136	class, in addition to any <b>boost::get_pointer</b> overloads.]
137	</p>
138	<p>
139	All function objects returned by <b>mem_fn</b> expose a <b>result_type</b> typedef
140	that represents the return type of the member function. For data members, <STRONG>result_type</STRONG>
141	is defined as the type of the member.
142	</p>
143	<h2><a name="FAQ">Frequently Asked Questions</a></h2>
144	<h3><a name="Q1">Can <b>mem_fn</b> be used instead of the standard <b>std::mem_fun[_ref]</b>
145	adaptors?</a></h3>
146	<p>
147	Yes. For simple uses, <b>mem_fn</b> provides additional functionality that the
148	standard adaptors do not. Complicated expressions that use <b>std::bind1st</b>, <b>std::bind2nd</b>
149	or <a href="../compose/index.htm"><b>Boost.Compose</b></a> along with the
150	standard adaptors can be rewritten using <a href="bind.html"><b>boost::bind</b></a>
151	that automatically takes advantage of <b>mem_fn</b>.
152	</p>
153	<h3><a name="Q2">Should I replace every occurence of <b>std::mem_fun[_ref]</b> with <b>mem_fn</b>
154	in my existing code?</a></h3>
155	<p>
156	No, unless you have good reasons to do so. <b>mem_fn</b> is not 100% compatible
157	with the standard adaptors, although it comes pretty close. In particular, <b>mem_fn</b>
158	does not return objects of type <b>std::[const_]mem_fun[1][_ref]_t</b>, as the
159	standard adaptors do, and it is not possible to fully describe the type of the
160	first argument using the standard <b>argument_type</b> and <b>first_argument_type</b>
161	nested typedefs. Libraries that need adaptable function objects in order to
162	function might not like <b>mem_fn</b>.
163	</p>
164	<h3><a name="Q3">Does <b>mem_fn</b> work with COM methods?</a></h3>
165	<p>
166	Yes, if you <a href="#stdcall">#define BOOST_MEM_FN_ENABLE_STDCALL</a>.
167	</p>
168	<h3><a name="Q4">Why isn't BOOST_MEM_FN_ENABLE_STDCALL defined automatically?</a></h3>
169	<p>
170	Non-portable extensions, in general, should default to off to prevent vendor
171	lock-in. Had BOOST_MEM_FN_ENABLE_STDCALL been defined automatically, you could
172	have accidentally taken advantage of it without realizing that your code is,
173	perhaps, no longer portable. In addition, it is possible for the default
174	calling convention to be __stdcall, in which case enabling __stdcall support
175	will result in duplicate definitions.
176	</p>
177	<h2><a name="Interface">Interface</a></h2>
178	<h3><a name="Synopsis">Synopsis</a></h3>
179	<pre>
180	namespace boost
181	{
182
183	template<class T> T * <a href="#get_pointer_1">get_pointer</a>(T * p);
184
185	template<class R, class T> <i>unspecified-1</i> <a href="#mem_fn_1">mem_fn</a>(R (T::*pmf) ());
186
187	template<class R, class T> <i>unspecified-2</i> <a href="#mem_fn_2">mem_fn</a>(R (T::*pmf) () const);
188
189	template<class R, class T> <i>unspecified-2-1</i> <a href="#mem_fn_2_1">mem_fn</a>(R T::*pm);
190
191	template<class R, class T, class A1> <i>unspecified-3</i> <a href="#mem_fn_3">mem_fn</a>(R (T::*pmf) (A1));
192
193	template<class R, class T, class A1> <i>unspecified-4</i> <a href="#mem_fn_4">mem_fn</a>(R (T::*pmf) (A1) const);
194
195	template<class R, class T, class A1, class A2> <i>unspecified-5</i> <a href="#mem_fn_5">mem_fn</a>(R (T::*pmf) (A1, A2));
196
197	template<class R, class T, class A1, class A2> <i>unspecified-6</i> <a href="#mem_fn_6">mem_fn</a>(R (T::*pmf) (A1, A2) const);
198
199	// implementation defined number of additional overloads for more arguments
200
201	}
202	</pre>
203	<h3><a name="CommonRequirements">Common requirements</a></h3>
204	<p>
205	All <tt><i>unspecified-N</i></tt> types mentioned in the Synopsis are <b>CopyConstructible</b>
206	and <b>Assignable</b>. Their copy constructors and assignment operators do not
207	throw exceptions. <tt><i>unspecified-N</i>::result_type</tt> is defined as the
208	return type of the member function pointer passed as an argument to <b>mem_fn</b>
209	(<b>R</b> in the Synopsis.) <tt><i>unspecified-2-1</i>::result_type</tt> is
210	defined as <tt>R</tt>.
211	</p>
212	<h3><a name="get_pointer">get_pointer</a></h3>
213	<h4><a name="get_pointer_1">template<class T> T * get_pointer(T * p)</a></h4>
214	<blockquote>
215	<p>
216	<b>Returns:</b> <tt>p</tt>.
217	</p>
218	<p>
219	<b>Throws:</b> Nothing.
220	</p>
221	</blockquote>
222	<h3><a name="mem_fn">mem_fn</a></h3>
223	<h4><a name="mem_fn_1">template<class R, class T> <i>unspecified-1</i> mem_fn(R
224	(T::*pmf) ())</a></h4>
225	<blockquote>
226	<p>
227	<b>Returns:</b> a function object <i>f</i> such that the expression <tt><i>f(t)</i></tt>
228	is equivalent to <tt>(t.*pmf)()</tt> when <i>t</i> is an l-value of type <STRONG>T </STRONG>
229	or derived, <tt>(get_pointer(t)->*pmf)()</tt> otherwise.
230	</p>
231	<p>
232	<b>Throws:</b> Nothing.
233	</p>
234	</blockquote>
235	<h4><a name="mem_fn_2">template<class R, class T> <i>unspecified-2</i> mem_fn(R
236	(T::*pmf) () const)</a></h4>
237	<blockquote>
238	<p>
239	<b>Returns:</b> a function object <i>f</i> such that the expression <tt><i>f(t)</i></tt>
240	is equivalent to <tt>(t.*pmf)()</tt> when <i>t</i> is of type <STRONG>T</STRONG>
241	<EM>[const]<STRONG> </STRONG></EM>or derived, <tt>(get_pointer(t)->*pmf)()</tt>
242	otherwise.
243	</p>
244	<p>
245	<b>Throws:</b> Nothing.
246	</p>
247	</blockquote>
248	<h4><a name="mem_fn_2_1">template<class R, class T> <i>unspecified-2-1</i> mem_fn(R
249	T::*pm)</a></h4>
250	<blockquote>
251	<p>
252	<b>Returns:</b> a function object <i>f</i> such that the expression <tt><i>f(t)</i></tt>
253	is equivalent to <tt>t.*pm</tt> when <i>t</i> is of type <STRONG>T</STRONG> <EM>[const]<STRONG>
254	</STRONG></EM>or derived, <tt>get_pointer(t)->*pm</tt> otherwise.
255	</p>
256	<p>
257	<b>Throws:</b> Nothing.
258	</p>
259	</blockquote>
260	<h4><a name="mem_fn_3">template<class R, class T, class A1> <i>unspecified-3</i> mem_fn(R
261	(T::*pmf) (A1))</a></h4>
262	<blockquote>
263	<p>
264	<b>Returns:</b> a function object <i>f</i> such that the expression <tt><i>f(t, a1)</i></tt>
265	is equivalent to <tt>(t.*pmf)(a1)</tt> when <i>t</i> is an l-value of type <STRONG>T
266	</STRONG>or derived, <tt>(get_pointer(t)->*pmf)(a1)</tt> otherwise.
267	</p>
268	<p>
269	<b>Throws:</b> Nothing.
270	</p>
271	</blockquote>
272	<h4><a name="mem_fn_4">template<class R, class T, class A1> <i>unspecified-4</i> mem_fn(R
273	(T::*pmf) (A1) const)</a></h4>
274	<blockquote>
275	<p>
276	<b>Returns:</b> a function object <i>f</i> such that the expression <tt><i>f(t, a1)</i></tt>
277	is equivalent to <tt>(t.*pmf)(a1)</tt> when <i>t</i> is of type <STRONG>T</STRONG>
278	<EM>[const]<STRONG> </STRONG></EM>or derived, <tt>(get_pointer(t)->*pmf)(a1)</tt>
279	otherwise.
280	</p>
281	<p>
282	<b>Throws:</b> Nothing.
283	</p>
284	</blockquote>
285	<h4><a name="mem_fn_5">template<class R, class T, class A1, class A2> <i>unspecified-5</i>
286	mem_fn(R (T::*pmf) (A1, A2))</a></h4>
287	<blockquote>
288	<p>
289	<b>Returns:</b> a function object <i>f</i> such that the expression <tt><i>f(t, a1, a2)</i></tt>
290	is equivalent to <tt>(t.*pmf)(a1, a2)</tt> when <i>t</i> is an l-value of type <STRONG>
291	T</STRONG> or derived, <tt>(get_pointer(t)->*pmf)(a1, a2)</tt> otherwise.
292	</p>
293	<p>
294	<b>Throws:</b> Nothing.
295	</p>
296	</blockquote>
297	<h4><a name="mem_fn_6">template<class R, class T, class A1, class A2> <i>unspecified-6</i>
298	mem_fn(R (T::*pmf) (A1, A2) const)</a></h4>
299	<blockquote>
300	<p>
301	<b>Returns:</b> a function object <i>f</i> such that the expression <tt><i>f(t, a1, a2)</i></tt>
302	is equivalent to <tt>(t.*pmf)(a1, a2)</tt> when <i>t</i> is of type <STRONG>T</STRONG>
303	<EM>[const]</EM> or derived, <tt>(get_pointer(t)->*pmf)(a1, a2)</tt> otherwise.
304	</p>
305	<p>
306	<b>Throws:</b> Nothing.
307	</p>
308	</blockquote>
309	<h2><a name="Implementation">Implementation</a></h2>
310	<h3><a name="Files">Files</a></h3>
311	<ul>
312	<li>
313	<a href="../../boost/mem_fn.hpp">boost/mem_fn.hpp</a>
314	(main header)
315	<li>
316	<a href="../../boost/bind/mem_fn_cc.hpp">boost/bind/mem_fn_cc.hpp</a>
317	(used by mem_fn.hpp, do not include directly)
318	<li>
319	<a href="../../boost/bind/mem_fn_vw.hpp">boost/bind/mem_fn_vw.hpp</a>
320	(used by mem_fn.hpp, do not include directly)
321	<li>
322	<a href="../../boost/bind/mem_fn_template.hpp">boost/bind/mem_fn_template.hpp</a>
323	(used by mem_fn.hpp, do not include directly)
324	<li>
325	<a href="test/mem_fn_test.cpp">libs/bind/test/mem_fn_test.cpp</a>
326	(test)
327	<li>
328	<a href="test/mem_fn_derived_test.cpp">libs/bind/test/mem_fn_derived_test.cpp</a>
329	(test with derived objects)
330	<li>
331	<a href="test/mem_fn_fastcall_test.cpp">libs/bind/test/mem_fn_fastcall_test.cpp</a>
332	(test for __fastcall)
333	<li>
334	<a href="test/mem_fn_stdcall_test.cpp">libs/bind/test/mem_fn_stdcall_test.cpp</a>
335	(test for __stdcall)
336	<li>
337	<a href="test/mem_fn_void_test.cpp">libs/bind/test/mem_fn_void_test.cpp</a> (test
338	for void returns)</li>
339	</ul>
340	<h3><a name="Dependencies">Dependencies</a></h3>
341	<ul>
342	<li>
343	<a href="../config/config.htm">Boost.Config</a></li>
344	</ul>
345	<h3><a name="NumberOfArguments">Number of Arguments</a></h3>
346	<p>
347	This implementation supports member functions with up to eight arguments. This
348	is not an inherent limitation of the design, but an implementation detail.
349	</p>
350	<h3><a name="stdcall">"__stdcall", "__cdecl" and "__fastcall" Support</a></h3>
351	<p>
352	Some platforms allow several types of member functions that differ by their <b>calling
353	convention</b> (the rules by which the function is invoked: how are
354	arguments passed, how is the return value handled, and who cleans up the stack
355	- if any.)
356	</p>
357	<p>
358	For example, Windows API functions and COM interface member functions use a
359	calling convention known as <b>__stdcall</b>. Borland VCL components use <STRONG>__fastcall</STRONG>.
360	UDK, the component model of OpenOffice.org, uses <STRONG>__cdecl</STRONG>.
361	</p>
362	<p>
363	To use <b>mem_fn</b> with <b>__stdcall</b> member functions, <b>#define</b> the
364	macro <b>BOOST_MEM_FN_ENABLE_STDCALL</b> before including, directly or
365	indirectly, <b><boost/mem_fn.hpp></b>.
366	</p>
367	<P>To use <B>mem_fn</B> with <B>__fastcall</B> member functions, <B>#define</B> the
368	macro <B>BOOST_MEM_FN_ENABLE_FASTCALL</B> before including <B><boost/mem_fn.hpp></B>.
369	</P>
370	<P>To use <B>mem_fn</B> with <B>__cdecl</B> member functions, <B>#define</B> the
371	macro <B>BOOST_MEM_FN_ENABLE_CDECL</B> before including <B><boost/mem_fn.hpp></B>.
372	</P>
373	<P><STRONG>It is best to define these macros in the project options, via -D on the
374	command line, or as the first line in the translation unit (.cpp file) where
375	mem_fn is used.</STRONG> Not following this rule can lead to obscure errors
376	when a header includes mem_fn.hpp before the macro has been defined.</P>
377	<P>[Note: this is a non-portable extension. It is not part of the interface.]
378	</P>
379	<p>
380	[Note: Some compilers provide only minimal support for the <b>__stdcall</b> keyword.]
381	</p>
382	<h2><a name="Acknowledgements">Acknowledgements</a></h2>
383	<p>
384	Rene Jager's initial suggestion of using traits classes to make <b>mem_fn</b> adapt
385	to user-defined smart pointers inspired the <b>get_pointer</b>-based design.
386	</p>
387	<p>
388	Numerous improvements were suggested during the formal review period by Richard
389	Crossley, Jens Maurer, Ed Brey, and others. Review manager was Darin Adler.
390	</p>
391	<p>
392	Steve Anichini pointed out that COM interfaces use <b>__stdcall</b>.
393	</p>
394	<p>
395	Dave Abrahams modified <b>bind</b> and <b>mem_fn</b> to support void returns on
396	deficient compilers.
397	</p>
398	<p>Daniel Boelzle pointed out that UDK uses <STRONG>__cdecl</STRONG>.<br>
399	<br>
400	<br>
401	<small>Copyright © 2001, 2002 by Peter Dimov and Multi Media Ltd. Copyright
402	2003-2005 Peter Dimov. Distributed under the Boost Software License, Version
403	1.0. See accompanying file <A href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</A> or
404	copy at <A href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>.</small></p>
405	</body>
406	</html>

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