cppdraft_translate/cppdraft/tuple/rel.md

[tuple.rel]

22 General utilities library [utilities]

22.4 Tuples [tuple]

22.4.9 Relational operators [tuple.rel]

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template<class... TTypes, class... UTypes> constexpr bool operator==(const tuple<TTypes...>& t, const tuple<UTypes...>& u); template<class... TTypes, [tuple-like](tuple.like#concept:tuple-like "22.4.3 Concept tuple-like [tuple.like]") UTuple> constexpr bool operator==(const tuple<TTypes...>& t, const UTuple& u);

1

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For the first overload let UTuple be tuple<UTypes...>.

2

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Constraints: For all i, where 0 ≤ i < sizeof...(TTypes),get(t) == get(u) is a valid expression anddecltype(get(t) == get(u)) models boolean-testable.

sizeof...(TTypes) equalstuple_size_v.

3

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Returns: true if get(t) == get(u) for alli, otherwise false.

[Note 1:

If sizeof...(TTypes) equals zero, returns true.

— end note]

4

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Remarks:

• (4.1)

  The elementary comparisons are performed in order from the zeroth index upwards. No comparisons or element accesses are performed after the first equality comparison that evaluates tofalse.

• (4.2)

  The second overload is to be found via argument-dependent lookup ([basic.lookup.argdep]) only.

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template<class... TTypes, class... UTypes> constexpr common_comparison_category_t<synth-three-way-result<TTypes, UTypes>...> operator<=>(const tuple<TTypes...>& t, const tuple<UTypes...>& u); template<class... TTypes, [tuple-like](tuple.like#concept:tuple-like "22.4.3 Concept tuple-like [tuple.like]") UTuple> constexpr common_comparison_category_t<synth-three-way-result<TTypes, Elems>...> operator<=>(const tuple<TTypes...>& t, const UTuple& u);

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For the second overload, Elems denotes the pack of typestuple_element_t<0, UTuple>,tuple_element_t<1, UTuple>, …,tuple_element_t<tuple_size_v - 1, UTuple>.

6

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Effects: Performs a lexicographical comparison between t and u.

If sizeof...(TTypes) equals zero, returns strong_ordering​::​equal.

Otherwise, equivalent to:if (auto c = synth-three-way(get<0>(t), get<0>(u)); c != 0) return c;return ttail <=> utail; where rtail for some r is a tuple containing all but the first element of r.

7

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Remarks: The second overload is to be found via argument-dependent lookup ([basic.lookup.argdep]) only.

8

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[Note 2:

The above definition does not require ttail (or utail) to be constructed.

It might not even be possible, as t and u are not required to be copy constructible.

Also, all comparison operator functions are short circuited; they do not perform element accesses beyond what is needed to determine the result of the comparison.

— end note]