23 General utilities library [utilities]

23.15 Metaprogramming and type traits [meta]

23.15.1 Requirements [meta.rqmts]

A UnaryTypeTrait describes a property of a type.
It shall be a class template that takes one template type argument and, optionally, additional arguments that help define the property being described.
It shall be DefaultConstructible, CopyConstructible, and publicly and unambiguously derived, directly or indirectly, from its base characteristic, which is a specialization of the template integral_­constant, with the arguments to the template integral_­constant determined by the requirements for the particular property being described.
The member names of the base characteristic shall not be hidden and shall be unambiguously available in the UnaryTypeTrait.
A BinaryTypeTrait describes a relationship between two types.
It shall be a class template that takes two template type arguments and, optionally, additional arguments that help define the relationship being described.
It shall be DefaultConstructible, CopyConstructible, and publicly and unambiguously derived, directly or indirectly, from its base characteristic, which is a specialization of the template integral_­constant, with the arguments to the template integral_­constant determined by the requirements for the particular relationship being described.
The member names of the base characteristic shall not be hidden and shall be unambiguously available in the BinaryTypeTrait.
A TransformationTrait modifies a property of a type.
It shall be a class template that takes one template type argument and, optionally, additional arguments that help define the modification.
It shall define a publicly accessible nested type named type, which shall be a synonym for the modified type.