Use template aliases to simplify notation and hide implementation details

Reason

Improved readability. Implementation hiding. Note that template aliases replace many uses of traits to compute a type. They can also be used to wrap a trait.

Example

template<typename T, size_t N>
class Matrix {
    // ...
    using Iterator = typename std::vector<T>::iterator;
    // ...
};

This saves the user of Matrix from having to know that its elements are stored in a vector and also saves the user from repeatedly typing typename std::vector<T>::.

Example

template<typename T>
void user(T& c)
{
    // ...
    typename container_traits<T>::value_type x; // bad, verbose
    // ...
}

template<typename T>
using Value_type = typename container_traits<T>::value_type;

This saves the user of Value_type from having to know the technique used to implement value_types.

template<typename T>
void user2(T& c)
{
    // ...
    Value_type<T> x;
    // ...
}

Note

A simple, common use could be expressed: "Wrap traits!"

Enforcement

• Flag use of typename as a disambiguator outside using declarations.
• ???