Are conditional typedef's possible in C++?

this question is related to c++

there is a library which declares a class named Solver < TS,FS >. Solver is a member of another class Domain (written by me)

now there are many Domains which have a member "int region"

what i want to do is depending on the value of region, I want to make the solver accept different arguments for TS and FS. I was thinking of something along the line

template<int region>
struct Decider
{
  if(region==1)
  {
     typedef TSA TS;
     typedef FSA FS;
  }
  else
  if(region==2)
  {
     typedef TSB TS;
     typedef FSB FS;
  }
}

and later use it as

Decider<region>::TS
Decider<region>::FS

However, here due to the scope of the if, i guess the struct is useless. However, I am not able to think of a better method to do this. Any suggestions?

All the different TS and FS have the same interface. So I don't have to worry about the inside code.