Modern C++ Programming Cookbook

How to do it...

The following list shows various situations where type traits are used to achieve various design goals:

• With enable_if, to define preconditions for the types a function template can be instantiated with:

        template <typename T,                  typename = typename std::enable_if<                        std::is_arithmetic<T>::value>::type>        T multiply(T const t1, T const t2)        {          return t1 * t2;        }        auto v1 = multiply(42.0, 1.5);     // OK        auto v2 = multiply("42"s, "1.5"s); // error

• With static_assert, to ensure that invariants are met:

        template <typename T>        struct pod_wrapper        {          static_assert(std::is_pod<T>::value, "Type is not a POD!");          T value;        };        pod_wrapper<int> i{ 42 };            // OK        pod_wrapper<std::string> s{ "42"s }; // error

• With std::conditional, to select between ...