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tutorial.xml: Add short discussion of the comparison of Boost.Function

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objects to function objects.


[SVN r21904]
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Douglas Gregor
2004-01-25 01:15:57 +00:00
parent c5d8d03b76
commit b7650282df
1 changed files with 33 additions and 1 deletions
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34
doc/tutorial.xml
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@ -274,7 +274,7 @@ f(&amp;x, 5);</programlisting>
</section>
<section>
<title>References to Functions</title> <para> In some cases it is
<title>References to Function Objects</title> <para> In some cases it is
expensive (or semantically incorrect) to have Boost.Function clone a
function object. In such cases, it is possible to request that
Boost.Function keep only a reference to the actual function
@ -321,5 +321,37 @@ using references to function objects, Boost.Function will not throw
exceptions during assignment or construction.
</para>
</section>
<section>
<title>Comparing Boost.Function function objects</title>
<para>Function object wrappers can be compared via <code>==</code>
or <code>!=</code> against any function object that can be stored
within the wrapper. If the function object wrapper contains a
function object of that type, it will be compared against the given
function object (which must be
<conceptname>EqualityComparable</conceptname>). For instance:</para>
<programlisting name="function.tutorial.compare">int compute_with_X(X*, int);
f = &amp;X::foo;
assert(f == &amp;X::foo);
assert(&amp;compute_with_X != f);</programlisting>
<para>When comparing against an instance of
<code><classname>reference_wrapper</classname></code>, the address
of the object in the
<code><classname>reference_wrapper</classname></code> is compared
against the address of the object stored by the function object
wrapper:</para>
<programlisting name="function.tutorial.compare-ref">a_stateful_object so1, so2;
f = <functionname>boost::ref</functionname>(so1);
assert(f == <functionname>boost::ref</functionname>(so1));
assert(f == so1); <emphasis>// Only if a_stateful_object is <conceptname>EqualityComparable</conceptname></emphasis>
assert(f != <functionname>boost::ref</functionname>(so2));</programlisting>
</section>
</section>