CODEWITHSUNDEEP
c++templatesoverloading
RandyGaul
RandyGaul

Reputation: 1915

Error C2893: Failed to specialize function template VC++ 2012

Given this code I have a compiler error I've had trouble solving:

struct TestType
{
  void PrintX( void )
  {
    printf( "TestType::PrintX : %d\n", x );
  }

  int x;
};

// Error here, BuildFunction overload not found
Function f = BuildFunction<decltype( &TestType::PrintX ), &TestType::PrintX>( &TestType::PrintX );

// Here is the overload
template <typename FunctionType, FunctionType *FunctionPtr, typename C>
Function BuildFunction( void (C::*fn)( void ) )
{
  return Function( fn, &CallMethodVoid<FunctionType, FunctionPtr, C> );
}

My exact error message is:

1>main.cpp(141): error C2893: Failed to specialize function
  template 'Function BuildFunction(void (__thiscall C::* )(void))'
1>          With the following template arguments:
1>          'void (__thiscall TestType::* )(void)'
1>          'TestType'

This code works just fine with static C functions (and the appropriate overloads), I just have this issue when trying to deal with a class or struct method. Any ideas on what the problem may be?

Upvotes: 1

Views: 1757

Answers (1)

mpark
mpark

Reputation: 7904

The problem lies in the type of the second template parameter of BuildFunction<>.

The first template parameter FunctionType, deduces to void (TestType::*)(void) since you've passed decltype(&TestType::PrintX) as the first template argument. The second template parameter as you specified it, reads FunctionType *. So the second template parameter is expecting a void (TestType::**)(void) (a pointer to a pointer to member function), which I don't think is what you intended. If you change the second template parameter to be FunctionType instead of FunctionType *, I think you'll get what you expect.

Upvotes: 4

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