C++ templates: Select different type based on value of template parameter

Question

How do I accomplish the following in C++, and what is doing such things called?

template 
class NuclearPowerplantControllerFactoryProviderFactory {         


        

Answer 1

By specialization:

template  class Foo;

template <> class Foo
{
  typedef int data_t;
};

template <> class Foo
{
  typedef unsigned int data_t;
};

You can choose to make one of the two cases the primary template and the other one the specialization, but I prefer this more symmetric version, given that bool can only have two values.

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_{If this is the first time you see this, you might also like to think about partial specialization:}

template  struct remove_pointer     { typedef T type; };
template  struct remove_pointer { typedef U type; };

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As @Nawaz says, the easiest way is probably to #include and say:

typedef typename std::conditional::type data_t;