c++ - How to check for the type of a template parameter?

Question

Suppose I have a template function and two classes

class animal {
}
class person {
}

template<class T>
void foo() {
  if (T is animal) {
    kill();
  }
}

How do I do the check for T is animal? I don't want to have something that checks during the run time. Thanks

Answer 1

Use is_same:

#include <type_traits>

template <typename T>
void foo()
{
    if (std::is_same<T, animal>::value) { /* ... */ }  // optimizable...
}

Usually, that's a totally unworkable design, though, and you really want to specialize:

template <typename T> void foo() { /* generic implementation  */ }

template <> void foo<animal>()   { /* specific for T = animal */ }

Note also that it's unusual to have function templates with explicit (non-deduced) arguments. It's not unheard of, but often there are better approaches.