std::remove_if using other class method

Question

I want to use std::remove_if with a predicate that is a member function of a differenct calss.

That is

class B;

class A {
    bool invalidB( const B& b ) const; // use members of class A to verify that B is invalid
    void someMethod() ;
};

Now, implementing A::someMethod, I have

void A::someMethod() {
    std::vector< B > vectorB; 
    // filling it with elements

    // I want to remove_if from vectorB based on predicate A::invalidB
    std::remove_if( vectorB.begin(), vectorB.end(), invalidB )
}

Is there a way to do this?

I have already looked into the solution of Idiomatic C++ for remove_if, but it deals with a slightly different case where the unary predicate of remove_if is a member of Band not A.

Moreover,
I do not have access to BOOST or c++11

Thanks!

Answer 1

Once you're in remove_if, you've lost the this pointer of A. So you'll have to declare a functional object which holds it, something like:

class IsInvalidB
{
    A const* myOwner;
public:
    IsInvalidB( A const& owner ) : myOwner( owner ) {}
    bool operator()( B const& obj )
    {
        return myOwner->invalidB( obj );
    }
}

Just pass an instance of this to remove_if.

Answer 2

If you don't want to create additional functors and you're restricted to C++03, use std::mem_fun_ref and std::bind1st:

std::remove_if(vectorB.begin(), vectorB.end(),
               std::bind1st(std::mem_fun_ref(&A::invalidB), some_A));

Alternatively, if your compiler supports TR1, you can use std::tr1::bind:

using std::tr1::placeholders::_1;
std::remove_if(vectorB.begin(), vectorB.end(),
               std::tr1::bind(&A::invalidB, some_A, _1));