[meta.logical]

21 Metaprogramming library [meta]

21.3 Metaprogramming and type traits [type.traits]

21.3.10 Logical operator traits [meta.logical]

This subclause describes type traits for applying logical operators to other type traits.

template<class... B> struct conjunction : see below { };

The class template conjunction forms the logical conjunction of its template type arguments.

For a specialization conjunction<, …, >, if there is a template type argument for which bool(::value) is false, then instantiating conjunction<, …, >::value does not require the instantiation of ::value for .

[Note 1:

This is analogous to the short-circuiting behavior of the built-in operator &&.

— end note]

Every template type argument for which ::value is instantiated shall be usable as a base class and shall have a member value which is convertible to bool, is not hidden, and is unambiguously available in the type.

The specialization conjunction<, …, > has a public and unambiguous base that is either

the first type in the list true_type, , …, for which bool(::value) is false, or
if there is no such , the last type in the list.

[Note 2:

This means a specialization of conjunction does not necessarily inherit from either true_type or false_type.

— end note]

The member names of the base class, other than conjunction and operator=, shall not be hidden and shall be unambiguously available in conjunction.

template<class... B> struct disjunction : see below { };

The class template disjunction forms the logical disjunction of its template type arguments.

For a specialization disjunction<, …, >, if there is a template type argument for which bool(::value) is true, then instantiating disjunction<, …, >::value does not require the instantiation of ::value for .

[Note 3:

This is analogous to the short-circuiting behavior of the built-in operator ||.

— end note]

The specialization disjunction<, …, > has a public and unambiguous base that is either

the first type in the list false_type, , …, for which bool(::value) is true, or
if there is no such , the last type in the list.

[Note 4:

This means a specialization of disjunction does not necessarily inherit from either true_type or false_type.

— end note]

The member names of the base class, other than disjunction and operator=, shall not be hidden and shall be unambiguously available in disjunction.

template<class B> struct negation : see below { };

The class template negation forms the logical negation of its template type argument.

The type negation<B> is a Cpp17UnaryTypeTrait with a base characteristic of bool_constant<!bool(B::value)>.