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      <td bgcolor="#FFFFFF"><img src="../../boost.png" alt=
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      "#FFFFFF"><big>More</big></font></a></td>
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  <h1>Improved Function Object Adapters</h1>

  <p>The header <a href="../../boost/functional.hpp">functional.hpp</a>
  provides enhancements to the function object adapters specified in the C++
  Standard Library (sections 20.3.5, through to 20.3.8). The enhancements are
  principally possible due to two changes:</p>

  <ol>
    <li>We use the Boost <tt><a href=
    "../utility/call_traits.htm">call_traits</a></tt> templates to avoid the
    problem of <a href="binders.html#refref">references to references</a>,
    and to improve the efficiency of <a href="mem_fun.html#args">parameter
    passing</a>.</li>

    <li>We use two <a href="function_traits.html">function object traits</a>
    class templates to avoid the need for <tt><a href=
    "ptr_fun.html">ptr_fun</a></tt> with the adapters in this library.</li>
  </ol>

  <h3>Contents</h3>

  <p>The header contains the following function and class templates:</p>

  <table border="1" cellpadding="5" summary="">
    <tr>
      <th align="left"><a href="function_traits.html">Function object
      traits</a></th>

      <td valign="top"><tt>unary_traits<br>
      binary_traits</tt></td>

      <td valign="top">Used to determine the types of function objects' and
      functions' arguments. Eliminate the necessity for
      <tt>ptr_fun</tt>.</td>
    </tr>

    <tr>
      <th align="left"><a href="negators.html">Negators</a></th>

      <td valign="top"><tt>unary_negate<br>
      binary_negate<br>
      not1<br>
      not2</tt></td>

      <td valign="top">Based on section 20.3.5 of the standard.</td>
    </tr>

    <tr>
      <th align="left"><a href="binders.html">Binders</a></th>

      <td valign="top"><tt>binder1st<br>
      binder2nd<br>
      bind1st<br>
      bind2nd</tt></td>

      <td valign="top">Based on section 20.3.6 of the standard.</td>
    </tr>

    <tr>
      <th align="left"><a href="ptr_fun.html">Adapters for pointers to
      functions</a></th>

      <td valign="top"><tt>pointer_to_unary_function<br>
      pointer_to_binary_function<br>
      ptr_fun</tt></td>

      <td valign="top">Based on section 20.3.7 of the standard. Not required
      for use with this library since the binders and negators can adapt
      functions, but may be needed with third party adapters.</td>
    </tr>

    <tr>
      <th align="left"><a href="mem_fun.html">Adapters for pointers to member
      functions</a></th>

      <td valign="top"><tt>mem_fun_t<br>
      mem_fun1_t<br>
      const_mem_fun_t<br>
      const_mem_fun1_t<br>
      mem_fun_ref_t<br>
      mem_fun1_ref_t<br>
      const_mem_fun_ref_t<br>
      const_mem_fun1_ref_t<br>
      mem_fun<br>
      mem_fun_ref</tt></td>

      <td valign="top">Based on section 20.3.8 of the standard.</td>
    </tr>

    <tr>
      <th align="left"><a href="identity.html">Identity</a></th>
      <td valign="top"><tt>identity</tt></td>
      <td valign="top">[func.identity] in ISO/IEC 14882:2020</td>
    </tr>
  </table>

  <h3>Usage</h3>

  <p>Using these adapters should be pretty much the same as using the
  standard function object adapters; the only differences are that you need
  to write <tt>boost::</tt> instead of <tt>std::</tt>, and that you will get
  fewer headaches.</p>

  <p>For example, suppose you had a <tt>Person</tt> class that contained a
  <tt>set_name</tt> function:</p>

  <blockquote>
    <pre>
class Person
{
  public:
    void set_name(const std::string &amp;name);
  // ...
};
</pre>
  </blockquote>

  <p>You could rename a bunch of people in a collection, <tt>c</tt>, by
  writing</p>

  <blockquote>
    <pre>
std::for_each(c.begin(), c.end(), 
              boost::bind2nd(boost::mem_fun_ref(&amp;Person::set_name), "Fred"));
</pre>
  </blockquote>

  <p>If the standard adapters had been used instead then this code would
  normally fail to compile, because <tt>set_name</tt> takes a reference
  argument. Refer to the comments in the <a href="binders.html#refref">binder
  documentation</a> to explain why this is so.</p>

  <h3>Compiler Compatibility</h3>

  <p>The header and <a href="test/function_test.cpp">test program</a> have been
  compiled with the following compilers:</p>

  <table border="1" cellpadding="5" summary="">
    <tr>
      <th>Compiler</th>

      <th>Comments</th>
    </tr>

    <tr>
      <td valign="top">Borland C++Builder 4 Update 2</td>

      <td valign="top">No known issues.</td>
    </tr>

    <tr>
      <td valign="top">Borland C++ 5.5</td>

      <td valign="top">No known issues.</td>
    </tr>

    <tr>
      <td valign="top">g++ 2.95.2</td>

      <td valign="top">No known issues.</td>
    </tr>

    <tr>
      <td valign="top">Microsoft Visual C++ Service Pack 3</td>

      <td valign="top">
        Compiler lacks partial specialisation, so this library offers little
        more than is provided by the standard adapters:

        <ul>
          <li>The <tt>call_traits</tt> mechanism is unable to prevent
          references to references, and so the adapters in this library will
          be usable in fewer situations.</li>

          <li>The <tt>function_traits</tt> mechanism is unable to determine
          the argument and result types of functions, therefore
          <tt>ptr_fun</tt> continues to be required to adapt functions.</li>
        </ul>
      </td>
    </tr>
  </table>

  <h3>Future Directions</h3>

  <p>This library's primary focus is to solve the problem of references to
  references while maintaining as much compatibility as possible with the
  standard library. This allows you to use the techniques you read about in
  books and magazines with many of today's compilers.</p>

  <p>In the longer term, even better solutions are likely:</p>

  <ol>
    <li>Several Boost members are working on expression template libraries.
    These will allow a more natural syntax for combining and adapting
    functions. As this is a new technology, it may be some time before it has
    matured and is widely supported by major compilers but shows great
    promise. In the meantime, the functional.hpp library fills the gap.</li>

    <li>The Standard Committee has recognised the problem of references to
    references occurring during template instantiation and has moved to fix
    the standard (see the <a href=
    "http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#106">C++
    standard core language active issues list</a>).</li>
  </ol>

  <h3>Author</h3>

  <p><a href="http://www.boost.org/people/mark_rodgers.htm">Mark Rodgers</a></p>

  <h3>Acknowledgements</h3>

  <p>Thanks to <a href="http://www.boost.org/people/john_maddock.htm">John Maddock</a> for
  suggesting the mechanism that allowed the function objects traits to work
  correctly. <a href="http://www.boost.org/people/jens_maurer.htm">Jens Maurer</a> provided
  invaluable feedback during the <a href=
  "http://www.boost.org/more/formal_review_process.htm">formal review process</a>.</p>
  <hr>

  <p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
  "../../doc/images/valid-html401.png" alt="Valid HTML 4.01 Transitional"
  height="31" width="88"></a></p>

  <p>Revised 
  <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->02
  December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38510" --></p>

  <p><i>Copyright &copy; 2000 Cadenza New Zealand Ltd.</i></p>

  <p><i>Distributed under the Boost Software License, Version 1.0. (See
  accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
  copy at <a href=
  "http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
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	8	<meta name="ProgId" content="FrontPage.Editor.Document">
	9
	10	<title>Boost Function Object Adapter Library</title>
	11	</head>
	12
	13	<body bgcolor="#FFFFFF" text="#000000">
	14	<table border="1" bgcolor="#007F7F" cellpadding="2" summary="">
	15	<tr>
	16	<td bgcolor="#FFFFFF"><img src="../../boost.png" alt=
	17	"boost.png (6897 bytes)" width="277" height="86"></td>
	18
	19	<td><a href="../../index.htm"><font face="Arial" color=
	20	"#FFFFFF"><big>Home</big></font></a></td>
	21
	22	<td><a href="../libraries.htm"><font face="Arial" color=
	23	"#FFFFFF"><big>Libraries</big></font></a></td>
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	25	<td><a href="http://www.boost.org/people/people.htm"><font face="Arial" color=
	26	"#FFFFFF"><big>People</big></font></a></td>
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	28	<td><a href="http://www.boost.org/more/faq.htm"><font face="Arial" color=
	29	"#FFFFFF"><big>FAQ</big></font></a></td>
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	31	<td><a href="../../more/index.htm"><font face="Arial" color=
	32	"#FFFFFF"><big>More</big></font></a></td>
	33	</tr>
	34	</table>
	35
	36	<h1>Improved Function Object Adapters</h1>
	37
	38	<p>The header <a href="../../boost/functional.hpp">functional.hpp</a>
	39	provides enhancements to the function object adapters specified in the C++
	40	Standard Library (sections 20.3.5, through to 20.3.8). The enhancements are
	41	principally possible due to two changes:</p>
	42
	43	<ol>
	44	<li>We use the Boost <tt><a href=
	45	"../utility/call_traits.htm">call_traits</a></tt> templates to avoid the
	46	problem of <a href="binders.html#refref">references to references</a>,
	47	and to improve the efficiency of <a href="mem_fun.html#args">parameter
	48	passing</a>.</li>
	49
	50	<li>We use two <a href="function_traits.html">function object traits</a>
	51	class templates to avoid the need for <tt><a href=
	52	"ptr_fun.html">ptr_fun</a></tt> with the adapters in this library.</li>
	53	</ol>
	54
	55	<h3>Contents</h3>
	56
	57	<p>The header contains the following function and class templates:</p>
	58
	59	<table border="1" cellpadding="5" summary="">
	60	<tr>
	61	<th align="left"><a href="function_traits.html">Function object
	62	traits</a></th>
	63
	64	<td valign="top"><tt>unary_traits<br>
65	binary_traits</tt></td>
66
67	<td valign="top">Used to determine the types of function objects' and
68	functions' arguments. Eliminate the necessity for
69	<tt>ptr_fun</tt>.</td>
70	</tr>
71
72	<tr>
73	<th align="left"><a href="negators.html">Negators</a></th>
74
75	<td valign="top"><tt>unary_negate<br>
76	binary_negate<br>
77	not1<br>
78	not2</tt></td>
79
80	<td valign="top">Based on section 20.3.5 of the standard.</td>
81	</tr>
82
83	<tr>
84	<th align="left"><a href="binders.html">Binders</a></th>
85
86	<td valign="top"><tt>binder1st<br>
87	binder2nd<br>
88	bind1st<br>
89	bind2nd</tt></td>
90
91	<td valign="top">Based on section 20.3.6 of the standard.</td>
92	</tr>
93
94	<tr>
95	<th align="left"><a href="ptr_fun.html">Adapters for pointers to
96	functions</a></th>
97
98	<td valign="top"><tt>pointer_to_unary_function<br>
99	pointer_to_binary_function<br>
100	ptr_fun</tt></td>
101
102	<td valign="top">Based on section 20.3.7 of the standard. Not required
103	for use with this library since the binders and negators can adapt
104	functions, but may be needed with third party adapters.</td>
105	</tr>
106
107	<tr>
108	<th align="left"><a href="mem_fun.html">Adapters for pointers to member
109	functions</a></th>
110
111	<td valign="top"><tt>mem_fun_t<br>
112	mem_fun1_t<br>
113	const_mem_fun_t<br>
114	const_mem_fun1_t<br>
115	mem_fun_ref_t<br>
116	mem_fun1_ref_t<br>
117	const_mem_fun_ref_t<br>
118	const_mem_fun1_ref_t<br>
119	mem_fun<br>
120	mem_fun_ref</tt></td>
121
122	<td valign="top">Based on section 20.3.8 of the standard.</td>
123	</tr>
1e59de90 TL	124
	125	<tr>
	126	<th align="left"><a href="identity.html">Identity</a></th>
	127	<td valign="top"><tt>identity</tt></td>
	128	<td valign="top">[func.identity] in ISO/IEC 14882:2020</td>
	129	</tr>
7c673cae FG	130	</table>
	131
	132	<h3>Usage</h3>
	133
	134	<p>Using these adapters should be pretty much the same as using the
	135	standard function object adapters; the only differences are that you need
	136	to write <tt>boost::</tt> instead of <tt>std::</tt>, and that you will get
	137	fewer headaches.</p>
	138
	139	<p>For example, suppose you had a <tt>Person</tt> class that contained a
	140	<tt>set_name</tt> function:</p>
	141
	142	<blockquote>
	143	<pre>
	144	class Person
	145	{
	146	public:
	147	void set_name(const std::string &name);
	148	// ...
	149	};
	150	</pre>
	151	</blockquote>
	152
	153	<p>You could rename a bunch of people in a collection, <tt>c</tt>, by
	154	writing</p>
	155
	156	<blockquote>
	157	<pre>
	158	std::for_each(c.begin(), c.end(),
	159	boost::bind2nd(boost::mem_fun_ref(&Person::set_name), "Fred"));
	160	</pre>
	161	</blockquote>
	162
	163	<p>If the standard adapters had been used instead then this code would
	164	normally fail to compile, because <tt>set_name</tt> takes a reference
	165	argument. Refer to the comments in the <a href="binders.html#refref">binder
	166	documentation</a> to explain why this is so.</p>
	167
	168	<h3>Compiler Compatibility</h3>
	169
	170	<p>The header and <a href="test/function_test.cpp">test program</a> have been
	171	compiled with the following compilers:</p>
	172
	173	<table border="1" cellpadding="5" summary="">
	174	<tr>
	175	<th>Compiler</th>
	176
	177	<th>Comments</th>
	178	</tr>
	179
	180	<tr>
	181	<td valign="top">Borland C++Builder 4 Update 2</td>
	182
	183	<td valign="top">No known issues.</td>
	184	</tr>
	185
	186	<tr>
	187	<td valign="top">Borland C++ 5.5</td>
	188
	189	<td valign="top">No known issues.</td>
	190	</tr>
	191
	192	<tr>
	193	<td valign="top">g++ 2.95.2</td>
194
195	<td valign="top">No known issues.</td>
196	</tr>
197
198	<tr>
199	<td valign="top">Microsoft Visual C++ Service Pack 3</td>
200
201	<td valign="top">
202	Compiler lacks partial specialisation, so this library offers little
203	more than is provided by the standard adapters:
204
205	<ul>
206	<li>The <tt>call_traits</tt> mechanism is unable to prevent
207	references to references, and so the adapters in this library will
208	be usable in fewer situations.</li>
209
210	<li>The <tt>function_traits</tt> mechanism is unable to determine
211	the argument and result types of functions, therefore
212	<tt>ptr_fun</tt> continues to be required to adapt functions.</li>
213	</ul>
214	</td>
215	</tr>
216	</table>
217
218	<h3>Future Directions</h3>
219
220	<p>This library's primary focus is to solve the problem of references to
221	references while maintaining as much compatibility as possible with the
222	standard library. This allows you to use the techniques you read about in
223	books and magazines with many of today's compilers.</p>
224
225	<p>In the longer term, even better solutions are likely:</p>
226
227	<ol>
228	<li>Several Boost members are working on expression template libraries.
229	These will allow a more natural syntax for combining and adapting
230	functions. As this is a new technology, it may be some time before it has
231	matured and is widely supported by major compilers but shows great
232	promise. In the meantime, the functional.hpp library fills the gap.</li>
233
234	<li>The Standard Committee has recognised the problem of references to
235	references occurring during template instantiation and has moved to fix
236	the standard (see the <a href=
237	"http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#106">C++
238	standard core language active issues list</a>).</li>
239	</ol>
240
241	<h3>Author</h3>
242
243	<p><a href="http://www.boost.org/people/mark_rodgers.htm">Mark Rodgers</a></p>
244
245	<h3>Acknowledgements</h3>
246
247	<p>Thanks to <a href="http://www.boost.org/people/john_maddock.htm">John Maddock</a> for
248	suggesting the mechanism that allowed the function objects traits to work
249	correctly. <a href="http://www.boost.org/people/jens_maurer.htm">Jens Maurer</a> provided
250	invaluable feedback during the <a href=
251	"http://www.boost.org/more/formal_review_process.htm">formal review process</a>.</p>
252	<hr>
253
254	<p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
255	"../../doc/images/valid-html401.png" alt="Valid HTML 4.01 Transitional"
256	height="31" width="88"></a></p>
257
258	<p>Revised
259	<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->02
260	December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38510" --></p>
261
262	<p><i>Copyright © 2000 Cadenza New Zealand Ltd.</i></p>
263
264	<p><i>Distributed under the Boost Software License, Version 1.0. (See
265	accompanying file <a href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
266	copy at <a href=
267	"http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
268	</body>
269	</html>