Returns true if this result is not successful or its value does not compares equal to the value in the success type sugar. Comparison is done using operator!= on value_type and A. If A is void, this call aliases bool has_error() const noexcept .

Requires: operator!= must be a valid expression between value_type and A, or A is void. If value_type is void, then so must be A.

Complexity: Whatever the underlying operator!= has. Constexpr and noexcept of underlying operations is propagated.

Guarantees: None.