It isn't removed, it's just deprecated in C++11. It's still part of the C++11 standard. You can still use it in your own code. It was removed in C++17 though.
It isn't used in the standard any more because requiring implementations to derive from binary_function
is over-specification.
Users should not care whether less
derives from binary_function
, they only need to care that it defines first_argument_type
, second_argument_type
and result_type
. It should be up to the implementation how it provides those typedefs.
Forcing the implementation to derive from a specific type means that users might start relying on that derivation, which makes no sense and is not useful.
Edit
How can we improve this in c++11 without unary_function?
You don't need it.
template<typename adaptableFunction>
class unary_negate
{
private:
adaptableFunction fun_;
public:
unary_negate(const adaptableFunction& f):fun_(f){}
template<typename T>
auto operator()(const T& x) -> decltype(!fun_(x))
{
return !fun_(x);
}
}
In fact you can do even better, see not_fn
: a generalized negator