Concept Subspace :: sus :: construct :: SafelyConstructibleFromReference

source

template <class To, class From>

concept SafelyConstructibleFromReference

requires

!__private::IsConstLvalueReference<To> ||

    // If the type is the same then no temporary will be created.

    std::same_as<std::remove_cvref_t<From>, std::remove_cvref_t<To>> ||

    // If the type is a base class then no temporary will be created.

    sus::ptr::SameOrSubclassOf<std::remove_cvref_t<From>*,

                                   std::remove_cvref_t<To>*>

Returns whether a type From is safely constructible from a reference of type To. If To is a const reference, then the types must match, as a conversion would create a reference to a temporary.

A struct will typically not actually store a reference but may provide an API of references nonetheless, and then store a pointer. When used with a universal reference From type, this can catch the case where the incoming reference will introduce a dangling reference when converted to the To reference.

Examples

template <std::convertible_to<i32&> U> requires(SafelyConstructibleFromReference<i32%, U&&> void Struct::stores_i32_ref(U&& u) { ptr_ = static_cast<i32&>(&u); }