Question

In the usual Strategy Pattern, we make each strategy as a class. Can’t we make it a function, and just assign the reference to the function when we instantiate an object, and let the object call that function?

Answer 1

In the simplest cases, you can replace Strategy patterns with a function pointer. However, consider this case

class HourlyPayStrategy implements PayStrategy
{
    public int calculate()
    {
        int x = doComplexOperation1();
        int y = doComplexOperation2();

        return x + y;
    }

    private int doComplexOperation1()
    {
        // ...
    }

    private int doComplexOperation2()
    {
        // ...
    }
}

If we just gave a simple function pointer, things start getting really hairy because you can no longer refactor that thing (well, at least not in an well encapsulated way).