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// { dg-do compile { target c++23 } }
// LWG 3886. Monad mo' problems
#include <expected>
void
test_constructor()
{
struct MoveOnly {
MoveOnly(int, int) { }
MoveOnly(MoveOnly&&) { }
};
// The {0,0} should be deduced as MoveOnly not const MoveOnly
[[maybe_unused]] std::expected<const MoveOnly, int> e({0,0});
}
struct Tracker {
bool moved = false;
constexpr Tracker(int, int) { }
constexpr Tracker(const Tracker&) { }
constexpr Tracker(Tracker&&) : moved(true) { }
// The follow means that is_assignable<const Tracker&, U> is true:
template<typename T> constexpr void operator=(T&&) const { }
// This stops a copy assignment from being declared implicitly:
void operator=(Tracker&) = delete;
};
void
test_assignment()
{
constexpr bool moved = [] {
std::expected<const Tracker, int> e(std::unexpect);
// The {0,0} should be deduced as Tracker not const Tracker:
e = {0,0};
// So the contained value should have been move constructed not copied:
return e->moved;
}();
static_assert( moved );
}
void
test_value_or()
{
constexpr bool moved = [] {
const std::expected<const Tracker, int> e(std::unexpect, 1);
return e.value_or({0,0}).moved;
}();
static_assert( moved );
constexpr bool moved_rval = [] {
std::expected<const Tracker, int> e(std::unexpect, 1);
return std::move(e).value_or({0,0}).moved;
}();
static_assert( moved_rval );
}
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