An Alias Template Specialization

Create a template alias

To show that a concept can be used to make sure that an alias template specialization names a type, let’s create a template alias, ValueTypeOf:

template<typename T> using ValueTypeOf = T::value_type;

Let’s use it in the concept TypeRequirement:

template<typename T>
concept TypeRequirement = requires {
    typename ValueTypeOf<T>;
};

Use the defined constraints

Let’s declare two variables with the constraint that we just defined, a vector of int values and an int.