20 General utilities library [utilities]

20.7 Variants [variant]

20.7.9 monostate relational operators [variant.monostate.relops]

constexpr bool operator==(monostate, monostate) noexcept { return true; } constexpr strong_ordering operator<=>(monostate, monostate) noexcept { return strong_ordering::equal; }
[Note:
monostate objects have only a single state; they thus always compare equal.
— end note]