17 Language support library [support]

17.11 Comparisons [cmp]

17.11.3 Class template common_­comparison_­category [cmp.common]

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The type common_­comparison_­category provides an alias for the strongest comparison category to which all of the template arguments can be converted.
[Note 1:
A comparison category type is stronger than another if they are distinct types and an instance of the former can be converted to an instance of the latter.
— end note]
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template<class... Ts> struct common_comparison_category { using type = see below; };
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Remarks: The member typedef-name type denotes the common comparison type ([class.spaceship]) of Ts..., the expanded parameter pack, or void if any element of Ts is not a comparison category type.
[Note 2:
This is std​::​strong_­ordering if the expansion is empty.
— end note]