Re: Covariant callback functions, or assigning base class members through a subclass reference

[Jacob Carlborg via Digitalmars-d-learn]

On 2015-07-14 17:53, Rene Zwanenburg wrote:

Sure, but that would make Base!Derived and Base!AnotherSubClass
different types.

What I'd like to end up with is a Base[], being able to call foo() on
the array members. Other parts of the code will add instances of derived
types to this array, and have set the callback function to a delegate
accepting said derived type.

You can add another base type that is not templated:

abstract class Base
{
    abstract void foo ();
}

abstract class TemplateBase(T) : Base
{
    alias CallbackType = void delegate(T);

    CallbackType callback;

    override void foo ()
    {
        callback(cast(T) this);
    }
}

class Derived : TemplateBase!(Derived)
{
    void derivedFunc()
    {
        import std.stdio;
        writeln("Derived object in action...");
    }
}

void main()
{
    auto d = new Derived();
    d.callback = (Derived d) { d.derivedFunc(); };
    Base[] bases = [d];
    foreach (b ; bases)
        b.foo();
}

--
/Jacob Carlborg