different class implementations based on template parameter

问题

I suppose this is trivial for people who know templates...

Suppose we want two different implementations of this template class, depending on the value of N:

template <int N>
class Foo {
    ...
};

For example:

template <int N>
class Foo {
    ... // implementation for N <= 10
};

template <int N>
class Foo {
    ... // implementation for N > 10
};

How can we do that in C++11?

回答1:

Use an extra template parameter with a default value to distinguish cases:

template <int N, bool b = N <= 10>
class Foo;

template <int N>
class Foo<N, true> {
  ...  // implementation for N <= 10
};

template <int N>
class Foo<N, false> {
  ...  // implementation for N > 10
};

来源：https://stackoverflow.com/questions/24491040/different-class-implementations-based-on-template-parameter