conditional (SFINAE) override

Question

I\'m trying to do this:

struct A
{
  virtual int f() const { return 0; }
};

template 
struct B : A
{
  template 

        

Answer 1

Try this:

template 
struct B : A
{
  ...
};

temlate 
struct B::type>:
  A
{
  virtual int f() const override { return 1; }
};

where we have two versions of B, one for which the condition is true (the enable_if one), one for which the condition is false (the default one).

If you wanted to be able to reuse your default B implementation, you could even do this:

template 
struct B : A
{
  ...
};

template 
struct B::type>:
  B
{
  virtual int f() const override { return 1; }
};

where we inherit from the "false" case in the "true" case. But that is a bit dirty to me -- I'd rather put the common implementation in some third spot (B_impl) rather than that hack. (That also lets you static assert that the second argument is void in the first case of B).