New Type Traits

This chapter presents several type traits (and two low-level functions for types) that C++20 introduces in its standard library.

Table New type traits lists these new type traits of C++20 (all are defined in the namespace std).

Trait		Effect
is_bounded_array_v<T>		Yields true if type T is an array type with known extent
is_unbounded_array_v<T>		Yields true if type T is an array type with unknown extent
is_nothrow_convertible_v<T, T2>		Yields true if T is convertible to type T2 without throwing
is_layout_compatible_v<T1, T2>		Yields true if T1 is layout-compatible with type T2
is_pointer_interconvertible...		Yields true if a pointer to DerT can safely be
_base_of_v<BaseT, DerT>		converted to a pointer to its base type BaseT
remove_cvref_t<T>		Yields type T without reference, top-level const, volatile
unwrap_reference_t<T>		Yields the wrapped type of type T if it is a
		std::reference_wrapper<> or otherwise T
unwrap_ref_decay_t<T>		Yields the wrapped type of type T if it is a
		std::reference_wrapper<> or otherwise its decayed type
common_reference_t<T...>		Yields the common type of all types T...
		to which you can assign a value
type_identity_t<T>		Yields type T as it is
iter_difference_t<T>		Yields the difference type of the incrementable/iterator type T
iter_value_t<T>		Yields the value/element type of the pointer/iterator type T
iter_reference_t<T>		Yields the reference type of the pointer/iterator type T
iter_rvalue_reference_t<T>		Yields the rvalue reference type of the pointer/iterator type T
is_clock_v<T>		Yields true if T is a clock type
compare_three_way_result_t<T>		Yields the type of comparing two values with operator <=>
	Table 20.1. New type traits

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