21 Metaprogramming library [meta]

21.3 Metaprogramming and type traits [type.traits]

21.3.7 Relationships between types [meta.rel]

Table 53: Type relationship predicates [tab:meta.rel]
Template
Condition
Comments
template<class T, class U>
struct is_same;
T and U name the same type with the same cv-qualifications
template<class Base, class Derived>
struct is_base_of;
Base is a base class of Derived ([class.derived]) without regard to cv-qualifiers or Base and Derived are not unions and name the same class type without regard to cv-qualifiers
If Base and Derived are non-union class types and are not (possibly cv-qualified versions of) the same type, Derived shall be a complete type.
[Note 1: 
Base classes that are private, protected, or ambiguous are, nonetheless, base classes.
— end note]
template<class Base, class Derived>
struct is_virtual_base_of;
Base is a virtual base class of Derived ([class.mi]) without regard to cv-qualifiers.
If Base and Derived are non-union class types, Derived shall be a complete type.
[Note 2: 
Virtual base classes that are private, protected, or ambiguous are, nonetheless, virtual base classes.
— end note]
[Note 3: 
A class is never a virtual base class of itself.
— end note]
template<class From, class To>
struct is_convertible;
see below
From and To shall be complete types, cv void, or arrays of unknown bound.
template<class From, class To>
struct is_nothrow_convertible;
is_convertible_v<From, To> is true and the conversion, as defined by is_convertible, is known not to throw any exceptions ([expr.unary.noexcept])
From and To shall be complete types, cv void, or arrays of unknown bound.
template<class T, class U>
struct is_layout_compatible;
T and U are layout-compatible ([basic.types.general])
T and U shall be complete types, cv void, or arrays of unknown bound.
template<class Base, class Derived>
struct is_pointer_interconvertible_base_of;
Derived is unambiguously derived from Base without regard to cv-qualifiers, and each object of type Derived is pointer-interconvertible ([basic.compound]) with its Base subobject, or Base and Derived are not unions and name the same class type without regard to cv-qualifiers.
If Base and Derived are non-union class types and are not (possibly cv-qualified versions of) the same type, Derived shall be a complete type.
template<class Fn, class... ArgTypes>
struct is_invocable;
The expression INVOKE(declval<Fn>(), declval<ArgTypes>()...) ([func.require]) is well-formed when treated as an unevaluated operand ([expr.context])
Fn and all types in the template parameter pack ArgTypes shall be complete types, cv void, or arrays of unknown bound.
template<class R, class Fn, class... ArgTypes>
struct is_invocable_r;
The expression INVOKE<R>(declval<Fn>(), declval<ArgTypes>()...) is well-formed when treated as an unevaluated operand
Fn, R, and all types in the template parameter pack ArgTypes shall be complete types, cv void, or arrays of unknown bound.
template<class Fn, class... ArgTypes>
struct is_nothrow_invocable;
is_invocable_v<
Fn, ArgTypes...> is true and the expression INVOKE(declval<Fn>(), declval<ArgTypes>()...) is known not to throw any exceptions ([expr.unary.noexcept])
Fn and all types in the template parameter pack ArgTypes shall be complete types, cv void, or arrays of unknown bound.
template<class R, class Fn, class... ArgTypes>
struct is_nothrow_invocable_r;
is_invocable_r_v<
R, Fn, ArgTypes...> is true and the expression INVOKE<R>(declval<Fn>(), declval<ArgTypes>()...) is known not to throw any exceptions ([expr.unary.noexcept])
Fn, R, and all types in the template parameter pack ArgTypes shall be complete types, cv void, or arrays of unknown bound.