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<title>Issue 798: Refactoring of binders lead to interface breakage</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#CD1">CD1</a> status.</em></p>
<h3 id="798"><a href="lwg-defects.html#798">798</a>. Refactoring of binders lead to interface breakage</h3>
<p><b>Section:</b> 99 [depr.lib.binders] <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Daniel Kr&uuml;gler <b>Opened:</b> 2008-02-14 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#depr.lib.binders">issues</a> in [depr.lib.binders].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2521.pdf">N2521</a>
and its earlier predecessors have moved the old binders from
[lib.binders] to 99 [depr.lib.binders] thereby introducing some renaming
of the template parameter names (<code>Operation -&gt; Fn</code>). During this
renaming process the <em>protected</em> data member <code>op</code> was also renamed to
<code>fn</code>, which seems as an unnecessary interface breakage to me - even if
this user access point is probably rarely used.
</p>


<p id="res-798"><b>Proposed resolution:</b></p>
<p>
Change  [depr.lib.binder.1st]:
</p>

<blockquote>
<pre>
template &lt;class Fn&gt; 
class binder1st 
  : public unary_function&lt;typename Fn::second_argument_type, 
                          typename Fn::result_type&gt; { 
protected: 
  Fn <del>fn</del> <ins>op</ins>; 
  typename Fn::first_argument_type value; 
public: 
  binder1st(const Fn&amp; x, 
            const typename Fn::first_argument_type&amp; y); 
  typename Fn::result_type 
    operator()(const typename Fn::second_argument_type&amp; x) const; 
  typename Fn::result_type 
    operator()(typename Fn::second_argument_type&amp; x) const; 
};
</pre>

<blockquote>
<p>
-1- The constructor initializes <del><code>fn</code></del> <ins><code>op</code></ins> with <code>x</code> and <code>value</code> with <code>y</code>.
</p>
<p>
-2- <code>operator()</code> returns <code><del>fn</del><ins>op</ins>(value,x)</code>.
</p>
</blockquote>
</blockquote>

<p>
Change  [depr.lib.binder.2nd]:
</p>

<blockquote>
<pre>
template &lt;class Fn&gt; 
class binder2nd
  : public unary_function&lt;typename Fn::first_argument_type, 
                          typename Fn::result_type&gt; { 
protected: 
  Fn <del>fn</del> <ins>op</ins>; 
  typename Fn::second_argument_type value; 
public: 
  binder2nd(const Fn&amp; x, 
            const typename Fn::second_argument_type&amp; y); 
  typename Fn::result_type 
    operator()(const typename Fn::first_argument_type&amp; x) const; 
  typename Fn::result_type 
    operator()(typename Fn::first_argument_type&amp; x) const; 
};
</pre>

<blockquote>
<p>
-1- The constructor initializes <del><code>fn</code></del> <ins><code>op</code></ins> with <code>x</code> and <code>value</code> with <code>y</code>.
</p>
<p>
-2- <code>operator()</code> returns <code><del>fn</del><ins>op</ins>(value,x)</code>.
</p>
</blockquote>
</blockquote>






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