20 General utilities library [utilities]

20.7 Variants [variant]

20.7.6 Relational operators [variant.relops]

template<class... Types>
  constexpr bool operator==(const variant<Types...>& v, const variant<Types...>& w);

Mandates: get(v) == get(w) is a valid expression that is convertible to bool, for all i.

Returns: If v.index() != w.index(), false; otherwise if v.valueless_by_exception(), true; otherwise get(v) == get(w) with i being v.index().

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template<class... Types>
  constexpr bool operator!=(const variant<Types...>& v, const variant<Types...>& w);

Mandates: get(v) != get(w) is a valid expression that is convertible to bool, for all i.

Returns: If v.index() != w.index(), true; otherwise if v.valueless_by_exception(), false; otherwise get(v) != get(w) with i being v.index().

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template<class... Types>
  constexpr bool operator<(const variant<Types...>& v, const variant<Types...>& w);

Mandates: get(v) < get(w) is a valid expression that is convertible to bool, for all i.

Returns: If w.valueless_by_exception(), false; otherwise if v.valueless_by_exception(), true; otherwise, if v.index() < w.index(), true; otherwise if v.index() > w.index(), false; otherwise get(v) < get(w) with i being v.index().

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template<class... Types>
  constexpr bool operator>(const variant<Types...>& v, const variant<Types...>& w);

Mandates: get(v) > get(w) is a valid expression that is convertible to bool, for all i.

Returns: If v.valueless_by_exception(), false; otherwise if w.valueless_by_exception(), true; otherwise, if v.index() > w.index(), true; otherwise if v.index() < w.index(), false; otherwise get(v) > get(w) with i being v.index().

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template<class... Types>
  constexpr bool operator<=(const variant<Types...>& v, const variant<Types...>& w);

Mandates: get(v) <= get(w) is a valid expression that is convertible to bool, for all i.

Returns: If v.valueless_by_exception(), true; otherwise if w.valueless_by_exception(), false; otherwise, if v.index() < w.index(), true; otherwise if v.index() > w.index(), false; otherwise get(v) <= get(w) with i being v.index().

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template<class... Types>
  constexpr bool operator>=(const variant<Types...>& v, const variant<Types...>& w);

Mandates: get(v) >= get(w) is a valid expression that is convertible to bool, for all i.

Returns: If w.valueless_by_exception(), true; otherwise if v.valueless_by_exception(), false; otherwise, if v.index() > w.index(), true; otherwise if v.index() < w.index(), false; otherwise get(v) >= get(w) with i being v.index().

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template<class... Types> requires (three_way_comparable<Types> && ...)
  constexpr common_comparison_category_t<compare_three_way_result_t<Types>...>
    operator<=>(const variant<Types...>& v, const variant<Types...>& w);

Effects: Equivalent to:

if (v.valueless_by_exception() && w.valueless_by_exception())
  return strong_ordering::equal;
if (v.valueless_by_exception()) return strong_ordering::less;
if (w.valueless_by_exception()) return strong_ordering::greater;
if (auto c = v.index() <=> w.index(); c != 0) return c;
return get<i>(v) <=> get<i>(w);

with i being v.index().