22 General utilities library [utilities]

22.4 Tuples [tuple]

22.4.9 Relational operators [tuple.rel]

template<class... TTypes, class... UTypes> constexpr bool operator==(const tuple<TTypes...>& t, const tuple<UTypes...>& u); template<class... TTypes, tuple-like UTuple> constexpr bool operator==(const tuple<TTypes...>& t, const UTuple& u);
For the first overload let UTuple be tuple<UTypes...>.
Mandates: For all i, where , get<i>(t) == get<i>(u) is a valid expression returning a type that is convertible to bool.
sizeof...(TTypes) equals tuple_­size_­v<UTuple>.
Returns: true if get<i>(t) == get<i>(u) for all i, otherwise false.
[Note 1:
If sizeof...(TTypes) equals zero, returns true.
— end note]
Remarks:
  • 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 to false.
  • The second overload is to be found via argument-dependent lookup ([basic.lookup.argdep]) only.
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 UTuple> constexpr common_comparison_category_t<synth-three-way-result<TTypes, Elems>...> operator<=>(const tuple<TTypes...>& t, const UTuple& u);
For the second overload, Elems denotes the pack of types tuple_­element_­t<0, UTuple>, tuple_­element_­t<1, UTuple>, …, tuple_­element_­t<tuple_­size_­v<UTuple> - 1, UTuple>.
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 <=> ; where for some r is a tuple containing all but the first element of r.
Remarks: The second overload is to be found via argument-dependent lookup ([basic.lookup.argdep]) only.
[Note 2:
The above definition does not require t (or u) 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 required to determine the result of the comparison.
— end note]