boostorg/functional
1
0
Fork 1
mirror of https://github.com/boostorg/functional.git synced 2025-07-29 20:17:19 +02:00
Code Issues Packages Projects Releases Wiki Activity

Add identity function object

Browse Source
This commit is contained in:
Glen Fernandes
2021-12-11 01:11:17 -05:00
parent 09d7a311a5
commit 0be868143d
6 changed files with 241 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

45
identity.html Normal file
View File

@ -0,0 +1,45 @@
<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Boost Function Object Adapter Library</title>
</head>
<body>
<h1>Identity</h1>
<p>The header <a href="../../boost/functional/identity.hpp">
&lt;boost/functional/identity.hpp&gt;</a> provides the function object
<code>boost::identity</code> whose <code>operator()</code> returns its
argument. It is an implementation of C++20's <code>std::identity</code>
that supports C++03 and above.</p>
<h2>Example</h2>
<p>It is commonly used as the default projection in constrained algorithms.</p>
<pre>
<code>template&lt;class Range, class Projection = boost::identity&gt;
void print(Range&& range, Projection projection = {});</code>
</pre>
<h2>Reference</h2>
<pre>
<code>namespace boost {
struct identity {
using is_transparent = <em>unspecified</em>;
template&lt;class T&gt;
T&amp;&amp; operator()(T&amp;&amp; value) const noexcept;
};
} // boost</code>
</pre>
<h3>Operators</h3>
<dl>
<dt><code>template&lt;class T&gt;
T&amp;&amp; operator()(T&amp;&amp; value) const noexcept;</code></dt>
<dd>Returns <code>std::forward&lt;T&gt;(value)</code></dd>
</dl>
<hr>
<p>Copyright 2021 Glen Joseph Fernandes.</p>
<p>Distributed under the
<a href="http://www.boost.org/LICENSE_1_0.txt">Boost Software License,
Version 1.0</a>.</p>
</body>
</html>

41
include/boost/functional/identity.hpp Normal file
View File

@ -0,0 +1,41 @@
/*
Copyright 2021 Glen Joseph Fernandes
(glenjofe@gmail.com)
Distributed under the Boost Software License, Version 1.0.
(http://www.boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_FUNCTIONAL_IDENTITY_HPP
#define BOOST_FUNCTIONAL_IDENTITY_HPP
#include <boost/config.hpp>
#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
#include <utility>
#endif
namespace boost {
struct identity {
typedef void is_transparent;
#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
template<class T>
BOOST_CONSTEXPR T&& operator()(T&& value) const BOOST_NOEXCEPT {
return std::forward<T>(value);
}
#else
template<class T>
BOOST_CONSTEXPR const T& operator()(const T& value) const BOOST_NOEXCEPT {
return value;
}
template<class T>
BOOST_CONSTEXPR T& operator()(T& value) const BOOST_NOEXCEPT {
return value;
}
#endif
};
} // boost
#endif

6
index.html
View File

@ -121,6 +121,12 @@
<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>

2
test/Jamfile.v2
View File

@ -6,4 +6,6 @@ import testing ;
test-suite functional :
[ run function_test.cpp ]
[ run identity_test.cpp ]
[ run identity_rvalue_test.cpp ]
;

75
test/identity_rvalue_test.cpp Normal file
View File

@ -0,0 +1,75 @@
/*
Copyright 2021 Glen Joseph Fernandes
(glenjofe@gmail.com)
Distributed under the Boost Software License, Version 1.0.
(http://www.boost.org/LICENSE_1_0.txt)
*/
#include <boost/config.hpp>
#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
#include <boost/functional/identity.hpp>
#include <boost/core/lightweight_test.hpp>
#include <algorithm>
#include <iterator>
#include <string>
#include <vector>
enum kind {
rvalue,
crvalue,
other
};
kind result(std::string&&)
{
return rvalue;
}
kind result(const std::string&&)
{
return crvalue;
}
template<class T>
kind result(T&&)
{
return other;
}
void simple_test()
{
typedef std::string string;
BOOST_TEST(boost::identity()(string("a")) == string("a"));
BOOST_TEST(result(boost::identity()(string("a"))) == rvalue);
typedef const std::string cstring;
BOOST_TEST(boost::identity()(cstring("a")) == cstring("a"));
BOOST_TEST(result(boost::identity()(cstring("a"))) == crvalue);
}
void algorithm_test()
{
std::vector<std::string> v1;
v1.push_back(std::string("a"));
v1.push_back(std::string("b"));
v1.push_back(std::string("c"));
std::vector<std::string> v2(v1);
std::vector<std::string> v3;
std::transform(std::make_move_iterator(v2.begin()),
std::make_move_iterator(v2.end()),
std::back_inserter(v3),
boost::identity());
BOOST_TEST(v3 == v1);
}
int main()
{
simple_test();
algorithm_test();
return boost::report_errors();
}
#else
int main()
{
return 0;
}
#endif

72
test/identity_test.cpp Normal file
View File

@ -0,0 +1,72 @@
/*
Copyright 2021 Glen Joseph Fernandes
(glenjofe@gmail.com)
Distributed under the Boost Software License, Version 1.0.
(http://www.boost.org/LICENSE_1_0.txt)
*/
#include <boost/functional/identity.hpp>
#include <boost/core/lightweight_test.hpp>
#include <algorithm>
#include <iterator>
#include <string>
#include <vector>
enum kind {
ref,
cref,
other
};
kind result(std::string&)
{
return ref;
}
kind result(const std::string&)
{
return cref;
}
template<class T>
kind result(T&)
{
return other;
}
template<class T>
kind result(const T&)
{
return other;
}
void simple_test()
{
std::string s1("a");
BOOST_TEST(boost::identity()(s1) == s1);
BOOST_TEST(&boost::identity()(s1) == &s1);
BOOST_TEST(result(boost::identity()(s1)) == ref);
const std::string s2("a");
BOOST_TEST(boost::identity()(s2) == s2);
BOOST_TEST(&boost::identity()(s2) == &s2);
BOOST_TEST(result(boost::identity()(s2)) == cref);
}
void algorithm_test()
{
std::vector<std::string> v1;
v1.push_back(std::string("a"));
v1.push_back(std::string("b"));
v1.push_back(std::string("c"));
std::vector<std::string> v2;
std::transform(v1.begin(), v1.end(), std::back_inserter(v2),
boost::identity());
BOOST_TEST(v2 == v1);
}
int main()
{
simple_test();
algorithm_test();
return boost::report_errors();
}