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POConditional enable an alternative assignment operator
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  1. POConditional enable an alternative assignment operator
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    copied!<p>I'm trying to conditionally instantiate an extra assignment operator. The code below works fine in clang, but not in gcc 4.7.</p> <p>The problem I'm having seems very similar the the question asked here: <a href="https://stackoverflow.com/questions/6972368/stdenable-if-to-conditionally-compile-a-member-function">std::enable_if to conditionally compile a member function</a></p> <p>The following illustrates the problem I'm having:</p> <pre><code>#include &lt;type_traits&gt; template&lt;typename T&gt; struct StrangerTypeRules; template&lt;typename T&gt; struct X; template&lt; &gt; struct StrangerTypeRules &lt; unsigned &gt; { typedef unsigned type; }; template&lt; &gt; struct StrangerTypeRules &lt; bool &gt; { typedef X&lt;bool&gt; type; }; template&lt;typename T&gt; struct X { // In the non-trivial version of my code, I can not use the // default assignment operator, therefor I need to define this one X&amp; operator=( const X&lt;T&gt;&amp; rhs ) { return *this; } // Alternative assignment oprtator, must only exists if it is // different from the assignment operator above template&lt;typename = typename std::enable_if&lt; ( !std::is_same&lt; X&lt;T&gt;, typename StrangerTypeRules&lt;T&gt;::type &gt;::value ), X&lt;T&gt; &gt;::type &gt; X&lt;T&gt; &amp; operator=( const typename StrangerTypeRules &lt;T&gt;::type&amp; rhs ) { return *this; } }; int main(int argc, const char *argv[]) { X&lt;unsigned&gt; x1, x2; x1 = 4; x2 = x1; X&lt;bool&gt; x3, x4; // compile error in gcc 4.7 with -std=c++11 //x3 = x4; return 0; } </code></pre> <p>Can this be done in a way which satisfies both clang and gcc 4.7? If so, how?</p> <p>Compilations error when using gcc:</p> <pre><code>test.cxx: In instantiation of ‘struct X&lt;bool&gt;’: test.cxx:52:13: required from here test.cxx:38:12: error: no type named ‘type’ in ‘struct std::enable_if&lt;false, X&lt;bool&gt; &gt;’ </code></pre>
 

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