Making Variant Greater Equal

Motivation

These edits align variant with optional in making the relational operators delegate to the relational operators of the underlying types

drive by fixes:

Other fixes, noticed when editing and/or suggested by LWG during review

• operator<() was defined as if index() was signed. It is not.
• convert Effects to Returns if...otherwise...otherwise... (as it was getting complicated)

?.6 Relational operators [variant.relops]

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

Requires:

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

Effects:

Equivalent to return (v.valueless_by_exception() && w.valueless_by_exception()) || (v.index() == w.index() && get<i>(v) == get<i>(w) with i being v.index().

Returns:

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

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

Requires:

get<i>(v) != get<i>(w) is a valid expression returning a type that is convertible to bool, for all i.

Effects:

Equivalent to return !(v == w).

Returns:

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

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

Requires:

get<i>(v) < get<i>(w) is a valid expression returning a type that is convertible to bool, for all i.

Effects:

Equivalent to return (v.index() < w.index()) || (v.index() == w.index() && !v.valueless_by_exception() && get<i>(v) < get<i>(w) with i being v.index().

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<i>(v) < get<i>(w) with i being v.index().

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

Requires:

get<i>(v) > get<i>(w) is a valid expression returning a type that is convertible to bool, for all i.

Effects:

Equivalent to return w < v.

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<i>(v) > get<i>(w) with i being v.index().

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

Requires:

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

Effects:

Equivalent to return !(v > w).

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<i>(v) <= get<i>(w) with i being v.index().

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

Requires:

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

Effects:

Equivalent to return !(v < w).

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<i>(v) >= get<i>(w) with i being v.index().