21 Metaprogramming library [meta]

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

For a specialization conjunction<${\text{B}}_1$, …, ${\text{B}}_N$>, if there is a template type argument ${\text{B}}_i$ for which bool(${\text{B}}_i$​::​value) is false, then instantiating conjunction<${\text{B}}_1$, …, ${\text{B}}_N$>​::​value does not require the instantiation of ${\text{B}}_j$​::​value for $j>i$.

Every template type argument for which ${\text{B}}_i$​::​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<${\text{B}}_1$, …, ${\text{B}}_N$> has a public and unambiguous base that is either

• (5.1)
  the first type ${\text{B}}_i$ in the list true_type, ${\text{B}}_1$, …, ${\text{B}}_N$ for which bool(${\text{B}}_i$​::​value) is false, or
• (5.2)
  if there is no such ${\text{B}}_i$, the last type in the list.

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

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

For a specialization disjunction<${\text{B}}_1$, …, ${\text{B}}_N$>, if there is a template type argument ${\text{B}}_i$ for which bool(${\text{B}}_i$​::​value) is true, then instantiating disjunction<${\text{B}}_1$, …, ${\text{B}}_N$>​::​value does not require the instantiation of ${\text{B}}_j$​::​value for $j>i$.

Every template type argument for which ${\text{B}}_i$​::​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 disjunction<${\text{B}}_1$, …, ${\text{B}}_N$> has a public and unambiguous base that is either

• (10.1)
  the first type ${\text{B}}_i$ in the list false_type, ${\text{B}}_1$, …, ${\text{B}}_N$ for which bool(${\text{B}}_i$​::​value) is true, or
• (10.2)
  if there is no such ${\text{B}}_i$, the last type in the list.

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

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)>.