predicates,

[vsgdp]

Why derive from: binary_function? It seems like that class just does some
typedefs.

For example, in Stroustrup (pg. 517 3rd edition):

class Club_eq : public unary_function<Club, bool> {
string s;
public:
explicit Club_eq(const string& ss) : s(ss) {}
bool operator()(const Club& c) const { return c.name == s; }
};

He still uses "Club" and "bool" instead of the typdefed argument_type and
result_type. So what is the point of these base classes?

 

[Victor Bazarov]

Why derive from: binary_function? It seems like that class just does
some typedefs.

You've answered your own question, I believe.

[..]

V

 

[vsgdp]

You've answered your own question, I believe.

No, what is the point of the typedefs?

 

[TB]

vsgdp skrev:

No, what is the point of the typedefs?

For example, the typedefs are used to propagate type data
within template expansions.

 

[Jerry Coffin]

Why derive from: binary_function? It seems like that class just does some
typedefs.

For example, in Stroustrup (pg. 517 3rd edition):

class Club_eq : public unary_function<Club, bool> {
string s;
public:
explicit Club_eq(const string& ss) : s(ss) {}
bool operator()(const Club& c) const { return c.name == s; }
};

He still uses "Club" and "bool" instead of the typdefed argument_type and
result_type. So what is the point of these base classes?

The typedefs aren't (at least primarily) for the benefit of the code
in the predicate itself. Rather, they're for use by the code in the
algorithm(s) to which you pass the predicate as an argument. The
typedefs give that code information about your predicate so the
predicate can be used correctly.