void assign(int val, const error_category& cat) noexcept;
Postconditions: val_ == val and
cat_ == &cat. template <class ErrorConditionEnum>
error_condition& operator=(ErrorConditionEnum e) noexcept;
Postconditions: *this == make_error_condition(e). Remarks: This operator shall not participate in overload resolution unless
is_error_condition_enum_v<ErrorConditionEnum> is
true. void clear() noexcept;
Postconditions: value() == 0 and
category() == generic_category().