Conditional compile-time inclusion/exclusion of code based on template argument(s)?

Question

Consider the following class, with the inner struct Y being used as a type, eg. in templates, later on:

template
class X{
  templat         


        

Answer 1

Can you try below (it is not partial specialization):

template
class X
{
};

template<>
class X<1>
{
  template
  struct Y{};
};

template<>
class X<2>
{
  template
  struct Y{};
};

I doubt if the answer is that simple !!

Edit (Mocking Partial specialization): @Xeo, I was able to compile following code and seems to be fullfilling.

template
struct X
{
  struct Unused {};  // this mocking structure will never be used

  template  // if 2 params passed-->ok; else default='Unused'
  struct Y{};

  template 
  struct Y{}; // This is specialization of above, define it your way
};

int main()
{
  X<1>::Y o1;  // Y called
  X<2>::Y o2; // Y called
}

Here, however you can use X<1>, X<2> interchangeably. But in the broader example you mentioned, that is irrelevant. Still if you need, you can put checks for I = 1 and I = 2.