Subject: [Boost-commit] svn:boost r64695 - trunk/libs/utility
From: daniel.j.walker_at_[hidden]
Date: 2010-08-09 12:07:33
Author: djwalker
Date: 2010-08-09 12:07:20 EDT (Mon, 09 Aug 2010)
New Revision: 64695
URL: http://svn.boost.org/trac/boost/changeset/64695
Log:
updated result_of documentation
Text files modified:
trunk/libs/utility/utility.htm | 101 +++++++++++++++++++++++++++++++--------
1 files changed, 80 insertions(+), 21 deletions(-)
Modified: trunk/libs/utility/utility.htm
==============================================================================
--- trunk/libs/utility/utility.htm (original)
+++ trunk/libs/utility/utility.htm 2010-08-09 12:07:20 EDT (Mon, 09 Aug 2010)
@@ -151,37 +151,96 @@
<code>result_of<F(T1, T2, ...,
T<em>N</em>)>::type</code> defines the result type
of the expression <code>f(t1, t2,
- ...,t<em>N</em>)</code>. The implementation permits
+ ...,t<em>N</em>)</code>. This implementation permits
the type <code>F</code> to be a function pointer,
function reference, member function pointer, or class
- type.</p> <p>If your compiler does not support
- <code>decltype</code>, then when <code>F</code> is a
- class type with a member type <code>result_type</code>,
+ type. By default, <em>N</em> may be any value between 0 and
+ 10. To change the upper limit, define the macro
+ <code>BOOST_RESULT_OF_NUM_ARGS</code> to the maximum
+ value for <em>N</em>. Class template <code>result_of</code>
+ resides in the header <code><<a
+ href="../../boost/utility/result_of.hpp">boost/utility/result_of.hpp</a>></code>.</p>
+
+ <p>If your compiler supports <code>decltype</code>,
+ then you can enable automatic result type deduction by
+ defining the macro <code>BOOST_RESULT_OF_USE_DECLTYPE</code>,
+ as in the following example.</p>
+
+ <blockquote>
+ <pre>#define BOOST_RESULT_OF_USE_DECLTYPE
+#include <boost/utility/result_of.hpp>
+
+struct functor {
+ template<class T>
+ T operator()(T x)
+ {
+ return x;
+ }
+};
+
+typedef boost::result_of<
+ functor(int)
+>::type type;</pre>
+ </blockquote>
+
+ <p>If your compiler does not support
+ <code>decltype</code>, then automatic result type
+ deduction of function objects is not
+ possible. Instead, <code>result_of</code>
+ uses the following protocol to allow the programmer to
+ specify a type. When <code>F</code> is a class type with a
+ member type <code>result_type</code>,
<code>result_of<F(T1, T2, ...,
T<em>N</em>)></code> is
- <code>F::result_type</code>. When <code>F</code>
- does not contain <code>result_type</code>,
+ <code>F::result_type</code>. When <code>F</code> does
+ not contain <code>result_type</code>,
<code>result_of<F(T1, T2, ...,
T<em>N</em>)></code> is <code>F::result<F(T1,
T2, ..., T<em>N</em>)>::type</code> when
<code><em>N</em> > 0</code> or <code>void</code>
- when <code><em>N</em> = 0</code>. For additional
- information about <code>result_of</code>, see the
- C++ Library Technical Report, <a
- href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf">N1836</a>,
- or, for motivation and design rationale, the <code>result_of</code> <a
- href="http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1454.html">proposal</a>.</p>
-
- <p>Class template <code>result_of</code> resides in
- the header <code><<a
- href="../../boost/utility/result_of.hpp">boost/utility/result_of.hpp</a>></code>. By
- default, <em>N</em> may be any value between 0 and
- 10. To change the upper limit, define the macro
- <code>BOOST_RESULT_OF_NUM_ARGS</code> to the maximum
- value for <em>N</em>.</p>
+ when <code><em>N</em> = 0</code>. Note that it is the
+ responsibility of the programmer to ensure that
+ function objects accurately advertise their result
+ type via this protocol, as in the following
+ example.</p>
+
+ <blockquote>
+ <pre>struct functor {
+ template<class> struct result;
+
+ template<class F, class T>
+ struct result<F(T)> {
+ typedef T type;
+ };
+
+ template<class T>
+ T operator()(T x)
+ {
+ return x;
+ }
+};
+
+typedef boost::result_of<
+ functor(int)
+>::type type;</pre>
+ </blockquote>
<a name="BOOST_NO_RESULT_OF"></a>
- <p>This implementation of <code>result_of</code> requires class template partial specialization, the ability to parse function types properly, and support for SFINAE. If <code>result_of</code> is not supported by your compiler, including the header <code>boost/utility/result_of.hpp</code> will define the macro <code>BOOST_NO_RESULT_OF</code>. Contributed by Doug Gregor.</p>
+ <p>This implementation of <code>result_of</code>
+ requires class template partial specialization, the
+ ability to parse function types properly, and support
+ for SFINAE. If <code>result_of</code> is not supported
+ by your compiler, including the header
+ <code>boost/utility/result_of.hpp</code> will
+ define the macro <code>BOOST_NO_RESULT_OF</code>.</p>
+
+ <p>For additional information
+ about <code>result_of</code>, see the C++ Library
+ Technical Report,
+ N1836,
+ or, for motivation and design rationale,
+ the <code>result_of</code> proposal.</p>
+ Contributed by Doug Gregor.</p>
<h2>Class templates for the Base-from-Member Idiom</h2>
<p>See separate documentation.</p>