From: dave@boostpro.com   
      
   on Tue Dec 27 2011, Kelvin Chung  wrote:   
      
   > I'm getting an unforseen problem when I'm trying to compile code for   
   > older compilers.  The following code compiles in clang 3.0 on a Mac:   
   >   
   > template    
   > struct Foo {   
   > 	typedef Key& key_type;   
   >   
   > 	virtual Bar mapKey(const key_type& key) = 0;   
   > };   
   >   
   > However, when I compile with gcc 4.1.2 on SUSE Linux, I get "cannot declare   
   reference to 'Key&', specifically wrt to mapKey().   
   >   
   > I'm trying to find the root cause of this: Is it a C++11-specifc   
   > thing,   
      
   Yes, reference-collapsing is a new feature in C++11.   
      
   > and thus barfing on gcc 4.1.2, which IIRC has no C++11 support?  Is it   
   > simply that I am expecting that "const key_type&" resolves to "Key&"   
   > (ie. the references "collapse"), when it shouldn't?  What should be   
   > the workaround for getting this snippet to compile under gcc 4.1.2?   
      
      virtual Bar mapKey(   
         const   
           typename remove_reference::type  // <== here   
         & key   
      ) = 0;   
      
   You can find remove_reference in Boost if it's not in gcc 4.1.2 in   
   namespace std::tr1 (I don't remember if they supply it in that version).   
      
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   Dave Abrahams   
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   http://www.boostpro.com   
      
      
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