Question

It is possible to store and wrap member functions with std::mem_fn?

In C you can use offsetof(...) on a data member to crudely wrap it (but only for some types). Is it possible to wrap a data member in C++? What’s the cleanest way?

For example:

class X
{
    ...
    M m;
    ...
};

mem_var<M> xm = &X::m;

int main()
{
    X x = ...;
    M i = ...;
    xm(x) = i; // same as x.m = i
    cout << xm(x); // same as cout << x.m
}

Answer 1

Yes, you can do it with… std::mem_fn.

struct B
{
    int x;
    int y;
};

int main()
{
    auto m = std::mem_fn(&B::y);

    B b {0, 0};
    m(b) = 4;

    printf("%d %d\n", b.x, b.y);    // prints 0 4
    printf("%d\n", m(b));           // prints 4

    return 0;
}

Demo: http://ideone.com/40nI2