[M3devel] calling an overridden method

[Hendrik Boom]

On Tue, Jul 19, 2011 at 07:11:05AM -0700, Mika Nystrom wrote:
> Sorry I'm being confusing here.
> 
> The code is right but I think your question is a bit confusing.
> 
> With your init example I don't think you're talking about an overridden
> init method but a shadowed method.

A 'shadowed' method.  Is that what you call what's essentially a new 
method that happens to have the same name?  Just like the way a variable 
in a nested block that has the same name as one in an outer block would 
be a new variable (I'm not sure Modula 3 allows this, the way C and the 
Algols do; I find it leads to confusing code).

Init is the one I've seen explained in documentation.  It's  not what I 
want, because that trick provides no inheritance.

> You can't call an overridden method
> through the widening trick, but you *can* call a shadowed method like
> that.
> 
>      Mika
> 
> Mika Nystrom writes:
> >
> >TYPE A = OBJECT METHODS m(xxx) END;
> >
> >TYPE B = A OBJECT METHODS m(xxx) END;

This is, if I understand the terminology, a declaratin of m as a shadowd 
method.  It's not what I want, because I  intend that under normal 
circumstances, if an B object is used in a context where its static type 
is known as A, I still want the normal overriding mechanism to ensure 
that B's m is the one called.

I mean something like

TYPE B = A OBJECT OVERRIDES m := ... END;

> >
> >b := NEW(B);
> >
> >A.m(b,xxx)

So this is a way to specifically get the m that belongs with A?  Will 
this work with the way I want to define B and m?

as in

TYPE A = OBJECT METHODS m(xxx) := bar END;

TYPE B = A OBJECT OVERRIDES m := foo END;

PROCEDURE foo(self : B, ....) =
BEGIN
  ...
  ...
   A.m(self, ...)   (* and this ends up calling bar? *)
  ...
END foo;

-- hendrik

> >
> >      Mika
> >
> >Hendrik Boom writes:
> >>I have a module containing a parent class, and another containing a 
> >>child class.
> >>
> >>The parent class contains a method 'foo', which is to be overridden in 
> >>the child class.
> >>
> >>But in implementing 'foo' in the child class I want to call the parent's 
> >>method.
> >>
> >>Now with the method 'init' there's a trick where in the child's init,
> >>you WIDEN self to the parent's type and then call its init.
> >>This works because 'init' isn't overridden in an OVERRIDES clause,
> >>but is defined as a new method that happens to have the same name.
> >>
> >>Is there any way to do this with 'foo', where the whole point is that
> >>it be an overridden method and not a new one?
> >>
> >>Do I have to do something like covertly exporting the PROCEDURE that 
> >>implements 'foo' in the parent's module so that it can be called 
> >>directly? That would seem to be a violation of modular design.  Or is 
> >>violating modular design exactly what I'm really trying to do here?
> >>
> >>-- hendrik