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

@Kerrek has answered the question sufficiently, but that can be more generic as follows:

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

And use as:

template 
class NuclearPowerplantControllerFactoryProviderFactory 
{
  typedef typename select::type data_t;
  //use data_t as data type
};

If S is true, the first type argument in select will be selected, or else second type argument will be selected. It is generic because you specify both types in select<>, and based on the value of the boolean, select::type returns either first type, or second type.