[fpc-pascal] Understanding virtual methods

Xiangrong Fang xrfang at gmail.com
Tue Aug 20 15:39:40 CEST 2013

Hi Sven,

Thank you for comment :)   I am interested in a high level description of
how these concepts (virtual / reintroduce / overloading) differs and how
they affect programming, and I am currently not running into trouble, just
try to get a better understanding of the language.

I'll explain my question / confusions:

1)  I didn't notice that my question are related to "modes" of fpc, i.e.
turbo-pascal/delphi/objfpc.    If they are different, I would like to know
more details, and I am more interested in objfpc mode, not those
"compatibility" modes.

2) I know override / overload are completely different thing, I am not
trying to compare apple with orange.   Also, I am clear about the
definition of virtual methods and their purpose.  What I need help is to
explain the observations I found with my demo app (which is a bit different
than I expected).  For example, why we need "reintroduce" while "overload"
does the same job and better (it makes both methods available)?


2013/8/20 Sven Barth <pascaldragon at googlemail.com>

> Am 20.08.2013 14:39 schrieb "Antonio Fortuny" <a.fortuny at sitasoftware.lu>:
> >
> >
> > Le 20/08/2013 14:34, Sven Barth a écrit :
> >>
> >> >>
> >> >> This is not same as the description in:
> http://www.freepascal.org/docs-html/ref/refsu26.html
> >> >>
> >> >> BTW, the above documents are talking about objects, but I am using
> classes, is there any difference here?
> >> >
> >> > Yep: a class is a construct definig a collection of variables,
> properties and methods whilst an object is an instantiated class.
> >>
> >> You are aware that the link mentioned by Xiangrong Fang points to a
> part of the manual about Turbo Pascal style objects which are different in
> a different sense to Delphi style objects/classes?
> >
> > Yes, but as he posts a question in a FPC list I imagine he is looking
> for some general information. He looks not to be in trouble. Lest's wait
> and see
> That has nothing to do with FPC list or not. Xiangrong Fang asked about
> two different language features here and you told him something about a
> completely different difference related to one of the two language features.
> Your answer is simply not an answer to his question.
> Regards,
> Sven
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