Type relationship safe_pointer_conversion

Type relationship `safe_pointer_conversion`

The safe_pointer_conversion type trait has the same syntax as std::is_constructible. It determines the behavior of safely_constructible for pointer types.

Valid Expressions

expression	value
`T, U`	any types
`safe_pointer_conversion<T, U>::value`	`true` if a `variant` for which `T` is one of the value types should be constructible from `U`.

Notes

To be "safe", converting U* to T* requires that T = U or const T = U.
Note that decay of T and U is implicit in the definition of safely_constructible. So this trait also governs conversions like const char * foo = "foo";.

Definition

template <typename A, typename B>
struct safe_pointer_conversion;

template <typename A, typename B>
struct safe_pointer_conversion<A *, B *> {
  static constexpr bool value = (std::is_same<A, B>::value || std::is_same<A, const B>::value)
                                && std::is_constructible<A *, B *>::value;
};

	Note
	You are welcome to specialize this trait to modify the behavior of `strict_variant`, but it might not always be the simplest way.