Variant: relational operators. (original) (raw)

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().