[concept.swappable] (original) (raw)

[Example 1:

User code can ensure that the evaluation of swap calls is performed in an appropriate context under the various conditions as follows:#include <cassert> #include <concepts> #include <utility> namespace ranges = std::ranges;template<class T, std::swappable_with<T> U> void value_swap(T&& t, U&& u) { ranges::swap(std::forward<T>(t), std::forward<U>(u));} template<std::swappable T> void lv_swap(T& t1, T& t2) { ranges::swap(t1, t2);} namespace N { struct A { int m; };struct Proxy { A* a; Proxy(A& a) : a{&a} {} friend void swap(Proxy x, Proxy y) { ranges::swap(*x.a, *y.a);} }; Proxy proxy(A& a) { return Proxy{ a }; } } int main() { int i = 1, j = 2; lv_swap(i, j); assert(i == 2 && j == 1); N::A a1 = { 5 }, a2 = { -5 }; value_swap(a1, proxy(a2)); assert(a1.m == -5 && a2.m == 5);}

— _end example_]