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Document the incompatibility that stems from Clang properly implement 

the rule that defines the implicit copy constructor/implicit copy
asssignment operator as deleted when a move constructor or move
assignment operator has been explicitly declared. This has hit a
number of people because Boost 1.47.0's shared_ptr fails to declare a
copy constructor.

llvm-svn: 140621
This commit is contained in:
Douglas Gregor 2011-09-27 18:58:27 +00:00
parent ed47406871
commit 244f7463cb
1 changed files with 39 additions and 1 deletions
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40
clang/www/compatibility.html
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@ -60,6 +60,12 @@
<li><a href="#param_name_lookup">Parameter name lookup</a></li>
</ul>
</li>
<li><a href="#c++11">C++11 compatibility</a>
<ul>
<li><a href="#deleted-special-func">Deleted special member
functions</a></li>
</ul>
</li>
<li><a href="#objective-c++">Objective-C++ compatibility</a>
<ul>
<li><a href="#implicit-downcasts">Implicit downcasts</a></li>
@ -755,7 +761,39 @@ void f(int a, int a);
<p>Clang diagnoses this error (where the parameter name has been redeclared). To fix this problem, rename one of the parameters.</p>
<!-- ======================================================================= -->
<h2 id="objective-c++">Objective-C++ compatibility</h3>
<h2 id="c++11">C++11 compatibility</h2>
<!-- ======================================================================= -->
<!-- ======================================================================= -->
<h3 id="deleted-special-func">Deleted special member functions</h3>
<!-- ======================================================================= -->
<p>In C++11, the explicit declaration of a move constructor or a move
assignment operator within a class disables the implicit declaration
of the copy constructor and copy assignment operator. This change came
fairly late in the C++11 standardization process, so early
implementations of C++11 (including Clang before 3.0, GCC before 4.7,
and Visual Studio 2010) do not implement this rule, leading them to
accept this ill-formed code:</p>
<pre>
struct X {
X(X&amp;&amp;); <i>// suppresses implicit copy constructor</i>
};
void f(X x);
void g(X x) {
f(x); <i>// error: X has no copy constructor</i>
}
</pre>
<p>This affects some C++11 code, including Boost's popular <a
href="http://www.boost.org/doc/libs/release/libs/smart_ptr/shared_ptr.htm"><tt>shared_ptr</tt></a>
up to version 1.47.0. The fix for Boost's <tt>shared_ptr</tt> is
<a href="https://svn.boost.org/trac/boost/changeset/73202">available here</a>.</p>
<!-- ======================================================================= -->
<h2 id="objective-c++">Objective-C++ compatibility</h2>
<!-- ======================================================================= -->
<!-- ======================================================================= -->