boost_mirror/utility
1
0
Fork 0
mirror of https://github.com/boostorg/utility.git synced 2025-05-09 15:04:00 +00:00
Code Issues Packages Projects Releases Wiki Activity

Fixed a bug in the semantics of less_pointees()

Browse Source 
[SVN r21132]
This commit is contained in:
Fernando Cacciola 2003-12-04 01:47:31 +00:00
parent 61fb5a0b8f
commit ec36cd8c54
2 changed files with 36 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
OptionalPointee.html
View File

@ -97,22 +97,50 @@ But boost::optional<T>, on the other hand, which is also a model of Option
deep-copy and deep-relational semantics.<br>
If generic code is written for this concept, it is important not to use relational
operators directly because the semantics might be different depending on the actual type.<br>
Still, the concept itsef can be used to define a <i>deep</i> equality-test that can
Still, the concept itsef can be used to define <i>deep</i> relational tests that can
be used in generic code with any type which models OptionalPointee:</p>
<a name="equal"></a>
<pre>
template&lt;class OptionalPointee&gt;
<p><u>Equivalence relation:</u></p>
<pre>template&lt;class OptionalPointee&gt;
inline
bool equal_pointees ( OptionalPointee const&amp; x, OptionalPointee const&amp; y )
{
return (!x) != (!y) ? false : ( !x ? true : (*x) == (*y) ) ;
}
template&lt;class OptionalPointee&gt;
struct equal_pointees_t : std::binary_function&lt;bool,OptionalPointee,OptionalPointee&gt;
{
bool operator() ( OptionalPointee const& x, OptionalPointee const& y ) const
{ return equal_pointees(x,y) ; }
} ;
</pre>
<p>The preceding generic function has the following semantics:<br>
If both x and y have valid pointees, it compares pointee's values via (*x == *y).<br>
<p>The preceding generic function and function object have the following semantics:<br>
If both x and y have valid pointees, it compares values via (*x == *y) or (*x &lt;
*y).<br>
If only one has a valid pointee, returns false.<br>
If both have invalid pointees, returns true.</p>
<p><code>equal_pointees()</code> is implemented in <a href="../../boost/optional.hpp">optional.hpp</a></p>
<a name="less"></a>
<p><u>Less-than relation:</u></p>
<pre>template&lt;class OptionalPointee&gt;
inline
bool less_pointees ( OptionalPointee const&amp; x, OptionalPointee const&amp; y )
{
return (!x) != (!y) ? false : ( !x ? false : (*x) == (*y) ) ;
}
template&lt;class OptionalPointee&gt;
struct less_pointees_t : std::binary_function&lt;bool,OptionalPointee,OptionalPointee&gt;
{
bool operator() ( OptionalPointee const& x, OptionalPointee const& y ) const
{ return less_pointees(x,y) ; }
} ;
</pre>
<p>The preceding generic function and function object have the following semantics:<br>
If both x and y have valid pointees, it compares values via (*x == *y) or (*x &lt;
*y).<br>
If only one has a valid pointee, returns false.<br>
If both have invalid pointees, returns false.</p>
<p>All these functions and function
objects are is implemented in <a href="../../boost/utility/compare_pointees.hpp">compare_pointees.hpp</a></p>
<p>Notice that OptionalPointee does not imply aliasing (and optional&lt;&gt; for instance does not alias);
so direct usage of relational operators with the implied aliasing of shallow semantics
-as with pointers- should not be used with generic code written for this concept.</p>

2
include/boost/utility/compare_pointees.hpp
View File

@ -52,7 +52,7 @@ template<class OptionalPointee>
inline
bool less_pointees ( OptionalPointee const& x, OptionalPointee const& y )
{
return !y ? false : ( !x ? true : (*x) < (*y) ) ;
return !y ? false : ( !x ? false : (*x) < (*y) ) ;
}
template<class OptionalPointee>