std::common_comparison_category

 

C++

Language

Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)
Dynamic memory management
Error handling
Program utilities
Variadic functions
Library feature-test macros
Date and time
Function objects
initializer_list (C++11)
bitset
hash (C++11)
integer_sequence (C++14)
Relational operators (deprecated)
rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
Comparisons (C++20)
strong_order weak_order partial_order strong_equal weak_equal	strong_ordering weak_ordering partial_ordering strong_equality weak_equality	is_eqis_neqis_ltis_lteqis_gtis_gteq
common_comparison_category
Common vocabulary types
pair tuple (C++11) apply (C++17) make_from_tuple (C++17)	optional (C++17) any (C++17) variant (C++17)
Swap, forward and move
swap
exchange (C++14)
forward (C++11)
move (C++11)
move_if_noexcept (C++11)
Elementary string conversions
to_chars (C++17)
from_chars (C++17)
chars_format (C++17)
Type operations
declval (C++11)
as_const (C++17)

 

Defined in header <compare>
template<class... Ts> struct common_comparison_category {   using type = /*see below*/ ; };		(since C++20)

The class template std::common_comparison_category provides an alias (as the member typedef type) for the strongest comparison category to which all of the template arguments Ts... can be converted.

In detail, the common comparison type of a list of n types T0...Tn-1 is defined as follows:

• If any Ti is not a comparison category type (std::weak_equality, std::strong_equality, std::partial_ordering, std::weak_ordering, std::strong_ordering), U is void.
• Otherwise, if at least one Ti is std::weak_equality or at least one Ti is std::strong_equality and at least one Ti is std::partial_ordering or std::weak_ordering, U is std::weak_equality
• Otherwise, if at least one Ti is std::strong_equality, U is std::strong_equality
• Otherwise, (if there is no std::weak_equality and no std::strong_equality) if at least one Ti is std::partial_ordering, U is std::partial_ordering
• Otherwise, if at least one Ti is std::weak_ordering, U is std::weak_ordering
• Otherwise (if every Ti is std::strong_ordering, or if the list is empty), U is std::strong_ordering.

Template parameters

...Ts

-

a possibly empty list of types

Helper template

template< class... Ts > using common_comparison_category_t = typename common_comparison_category<Ts...>::type;		(since C++20)

Member types

Member type	Definition
type	the strongest common comparison category (as defined above)

See also

strong_ordering (C++20)	the result type of 3-way comparison that supports all 6 operators and is substitutable (class)
weak_ordering (C++20)	the result type of 3-way comparison that supports all 6 operators and is not substitutable (class)
partial_ordering (C++20)	the result type of 3-way comparison that supports all 6 operators, is not substitutable, and allows incomparable values (class)
strong_equality (C++20)	the result type of 3-way comparison that supports only equality/inequality and is substitutable (class)
weak_equality (C++20)	the result type of 3-way comparison that supports only equality/inequality and is not substitutable (class)