std::common_comparison_category

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Utilities library

Language support

Type support (basic types, RTTI)

Library feature-test macros(C++20)

Program utilities

Variadic functions

initializer_list

(C++11)

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(C++20)

is_within_lifetime

(C++26)

source_location

(C++20)

Coroutine support(C++20)

Contract support(C++26)

Three-way comparison

three_way_comparablethree_way_comparable_with

(C++20)(C++20)

strong_ordering

(C++20)

weak_ordering

(C++20)

partial_ordering

(C++20)

common_comparison_category

(C++20)

compare_three_way_result

(C++20)

(C++20)

(C++20)

(C++20)

(C++20)

compare_strong_order_fallback

(C++20)

compare_weak_order_fallback

(C++20)

compare_partial_order_fallback

(C++20)

is_eqis_ltis_lteq

(C++20)(C++20)(C++20)

is_neqis_gtis_gteq

(C++20)(C++20)(C++20)

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rel_ops::operator<=rel_ops::operator>=

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cmp_equalcmp_lesscmp_less_than

(C++20)(C++20)(C++20)

cmp_not_equalcmp_greatercmp_greater_than

(C++20)(C++20)(C++20)

in_range

(C++20)

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swap
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Common vocabulary types

pair
tuple (C++11)
optional (C++17)
any (C++17)
variant (C++17)

tuple_size (C++11)
tuple_element (C++11)
apply (C++17)
make_from_tuple (C++17)
expected (C++23)

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

The class templatestd::common_comparison_category provides an alias (as the member typedeftype) for the strongest comparison category to which all of the template argumentsTs... can be converted.

In detail, the common comparison type of a list of n typesT₀...T_n-1 is defined as follows:

If anyT_i is not a comparison category type (std::partial_ordering,std::weak_ordering,std::strong_ordering),U isvoid.
Otherwise, if at least oneT_i isstd::partial_ordering,U isstd::partial_ordering.
Otherwise, if at least oneT_i isstd::weak_ordering,U isstd::weak_ordering.
Otherwise (if everyT_i isstd::strong_ordering, or if the list is empty),U isstd::strong_ordering.

[edit]Template parameters

...Ts

a possibly empty list of types

[edit]Helper template

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

[edit]Member types

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

[edit]Possible implementation

namespace detail{template<unsignedint>struct common_cmpcat_base{using type=void;};template<>struct common_cmpcat_base<0u>{using type=std::strong_ordering;};template<>struct common_cmpcat_base<2u>{using type=std::partial_ordering;};template<>struct common_cmpcat_base<4u>{using type=std::weak_ordering;};template<>struct common_cmpcat_base<6u>{using type=std::partial_ordering;};}// namespace detail template<class...Ts>struct common_comparison_category:    detail::common_cmpcat_base<(0u| ...|(std::is_same_v<Ts,std::strong_ordering>? 0u:std::is_same_v<Ts,std::weak_ordering>? 4u:std::is_same_v<Ts,std::partial_ordering>? 2u: 1u))>{};

[edit]Example

This section is incomplete
Reason: no example

[edit]See also

strong_ordering (C++20)	the result type of 3-way comparison that supports all 6 operators and is substitutable (class)[edit]
weak_ordering (C++20)	the result type of 3-way comparison that supports all 6 operators and is not substitutable (class)[edit]
partial_ordering (C++20)	the result type of 3-way comparison that supports all 6 operators, is not substitutable, and allows incomparable values (class)[edit]