TypeFeature (named requirement)

Requirements

A type F is a TypeFeature if:

• F satisfies LiteralType
• F::make<T>() is valid as constant expression that returns an instance of F bound to the target type T

Notes

A type feature is a class that captures and exposes a specific property or action of a target type, without depending from it at compile time. Most times features store a pointer to a function (that is like an entry in a vtable), but they may hold just data (like f_size and f_alignment do).

Usually a TypeFeature has this form:

struct f_feature
{
    // returns an instance of this feature bound to a specific target type
    template <typename TARGET_TYPE>
        constexpr static type make() noexcept;

    // invokes the feature. The return type and the parameters depends on the specific feature
    ... operator()(...) const;
};

The static function template make creates an instance of the feature bound to a type. The function call operator invokes the feature.

The following snippet shows the synopsis of f_size, f_default_construct and f_equal.

struct f_size
{
    template <typename TARGET_TYPE>
        constexpr static f_size make() noexcept;

    constexpr size_t operator()() const noexcept;
};

struct f_default_construct
{
    template <typename TARGET_TYPE>
        constexpr static f_default_construct make() noexcept;

    void operator()(void * i_dest) const;
};

struct f_equal
{
    template <typename TARGET_TYPE>
        constexpr static f_equal make() noexcept;
    bool operator()(void const * i_first, void const * i_second) const;
};