c++ - Is it considered "correct" to use a template for a function/class that only accepts subclasses of a specific class?

Question

Lets say hypothetically that I am making a game and in that game there are spawning points class SpawnArea for monsters' classes that inherit from class Monster. Would it be correct to use a template knowing that I am not expecting just any class and Spawn will only accept a specific subset of classes? I would like to use a template cause it's the only way I'm aware of to pass a class type as argument for the purpose of constructing instances of a specific class. Is there any more elegant way to write a class who's instances are used to construct multiple instances of some other specific class?

I read this:

Make a template accept a specific class/family of classes?

It did not discuss the issue of constructing instances of a specific set of classes.

Answer 1

It's quite common, actually almost all templates have certain requirements towards their arguments. Those are usually implicitly clear from how the template parameter is used, but you can improve the error messages by using type traits. In C++11, they are available from the standard library via #include <type_traits>, otherwise look into Boost.TypeTraits.

With C++11, the usage is quite simple when you also use static_assert:

template< typename T >
std::shared_ptr< T > spawn()
{
    // make this the first line in your function to get errors early.
    // also note that you can use any compile-time check you like.
    static_assert( std::is_base_of< Monster, T >::value,
                   "T is not derived from Monster" );

    // the rest of your code follows here.
    // ...
    // return ...;
}