20 General utilities library [utilities]

20.4 Tuples [tuple]

20.4.2 Class template tuple [tuple.tuple]

20.4.2.7 Relational operators [tuple.rel]

template<class... TTypes, class... UTypes> bool operator==(const tuple<TTypes...>& t, const tuple<UTypes...>& u);

1

Requires: For all i, where 0 <= i and i < sizeof...(Types), get<i>(t) == get<i>(u) is a valid expression returning a type that is convertible to bool. sizeof...(TTypes) == sizeof...(UTypes).

2

Returns: true iff get<i>(t) == get<i>(u) for all i. For any two zero-length tuples e and f, e == f returns true.

3

Effects: 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.

template<class... TTypes, class... UTypes> bool operator<(const tuple<TTypes...>& t, const tuple<UTypes...>& u);

4

Requires: For all i, where 0 <= i and i < sizeof...(Types), get<i>(t) < get<i>(u) and get<i>(u) < get<i>(t) are valid expressions returning types that are convertible to bool. sizeof...(TTypes) == sizeof...(UTypes).

5

Returns: The result of a lexicographical comparison between t and u. The result is defined as: (bool)(get<0>(t) < get<0>(u)) || (!(bool)(get<0>(u) < get<0>(t)) && ttail < utail), where rtail for some tuple r is a tuple containing all but the first element of r. For any two zero-length tuples e and f, e < f returns false.

template<class... TTypes, class... UTypes> bool operator!=(const tuple<TTypes...>& t, const tuple<UTypes...>& u);

6

Returns: !(t == u).

template<class... TTypes, class... UTypes> bool operator>(const tuple<TTypes...>& t, const tuple<UTypes...>& u);

7

Returns: u < t.

template<class... TTypes, class... UTypes> bool operator<=(const tuple<TTypes...>& t, const tuple<UTypes...>& u);

8

Returns: !(u < t)

template<class... TTypes, class... UTypes> bool operator>=(const tuple<TTypes...>& t, const tuple<UTypes...>& u);

9

Returns: !(t < u)

10

[ Note: The above definitions for comparison operators do not require ttail (or utail) to be constructed. It may not even be possible, as t and u are not required to be copy constructible. Also, all comparison operators are short circuited; they do not perform element accesses beyond what is required to determine the result of the comparison.  — end note ]