Template specialization problem

[Onur Cobanoglu]

Hi,

I have some user-defined classes, for which I have to define std::hash, which are nested in the scope of another user-defined class. So I have to specialize hash<> for those. The problem is that:

1-) I cannot do the specialization before the outer class declaration, because if template parameters are classes then they should be fully declared previously (forward declaration does not work).
2-) I cannot do the specialization after the outer class declaration, because I'm using the specialized hash<> classes within the scope of the outer class declaration and I'm getting a 'specialization after instantiation' error by the compiler.
3-) I cannot do the specialization within the scope of the outer class, because hash<> is defined in namespace std and the compiler gives the error that template is specialized in non-namespace scope. When I try to enclose the specializations with

namespace std {}

It gives me a weird error saying that "expected unqualified-id before ‘namespace’".

So I'm stuck, and I don't know how to do these specializations. My full code is too long to include but here are the snippets relevant to the problem:

class BPCFGParser {
  public:

  ...
  ...

  class Edge {
    ...
    ...
  };


  class ActiveEquivClass {
    ...
    ...
  };

  class PassiveEquivClass {
    ...
    ...
  };

  struct EqActiveEquivClass {
    ...
    ...
  };

  struct EqPassiveEquivClass {
    ...
    ...
  };



  unordered_map<ActiveEquivClass, Edge *, hash<ActiveEquivClass>, EqActiveEquivClass> discovered_active_edges;
  unordered_map<PassiveEquivClass, Edge *, hash<PassiveEquivClass>, EqPassiveEquivClass> discovered_passive_edges;

};

In this code I'm trying to specialize std::hash<> for ActiveEquivClass and PassiveEquivClass. I'm working with g++ on Linux, with -std=gnu++0x option. Any help will be highly appreciated. Thanks.