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<title>Issue 362: bind1st/bind2nd type safety</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="362"><a href="lwg-defects.html#362">362</a>. bind1st/bind2nd type safety</h3>
<p><b>Section:</b> 99 [depr.lib.binders] <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Andrew Demkin <b>Opened:</b> 2002-04-26 <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>
The definition of bind1st() (99 [depr.lib.binders]) can result in
the construction of an unsafe binding between incompatible pointer
types. For example, given a function whose first parameter type is
'pointer to T', it's possible without error to bind an argument of
type 'pointer to U' when U does not derive from T:
</p>
<pre>
   foo(T*, int);

   struct T {};
   struct U {};

   U u;

   int* p;
   int* q;

   for_each(p, q, bind1st(ptr_fun(foo), &amp;u));    // unsafe binding
</pre>

<p>
The definition of bind1st() includes a functional-style conversion to
map its argument to the expected argument type of the bound function
(see below):
</p>
<pre>
  typename Operation::first_argument_type(x)
</pre>

<p>
A functional-style conversion (99 [depr.lib.binders]) is defined to be
semantically equivalent to an explicit cast expression (99 [depr.lib.binders]), which may (according to 5.4, paragraph 5) be interpreted
as a reinterpret_cast, thus masking the error.
</p>

<p>The problem and proposed change also apply to 99 [depr.lib.binders].</p>


<p id="res-362"><b>Proposed resolution:</b></p>
<p>Add this sentence to the end of 99 [depr.lib.binders]/1:
  "Binders <code>bind1st</code> and <code>bind2nd</code> are deprecated in
  favor of <code>std::tr1::bind</code>."</p>

<p>(Notes to editor: (1) when and if tr1::bind is incorporated into
  the standard, "std::tr1::bind" should be changed to "std::bind". (2)
  20.5.6 should probably be moved to Annex D.</p>


<p><b>Rationale:</b></p>
<p>There is no point in fixing bind1st and bind2nd.  tr1::bind is a
  superior solution.  It solves this problem and others.</p>





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