[Lazarus] How do you create some kind of type definition based on adding a set if identical functions to different objects with different ancestors?

Max Vlasov max.vlasov at gmail.com
Fri Nov 19 22:10:46 CET 2010

2010/11/19 Frank Church <vfclists at gmail.com>

> On 17 November 2010 10:39, Frank Church <vfclists at gmail.com> wrote:
>> I don't know whether interfaces are what I am looking for here.
>> I am creating an object called TStateInfoSource which needs to display its
>> state using different objects, mainly a TForm, a TFrame, some future
>> TComponent based visual object and a  web interface as yet undecided.
>> eg, both the TForm, the TFrame and web object are to implement a function
>> called DisplayState in their own way.
>> Is there some way to create some kind of type definition called a
>> TImplementsDisplayState so that TStateInfoSource can call the DisplayState
>> function of  TImplementsDisplayState object it is associated with at
>> runtime?
>> In effect the TImplementsDisplayState facility is added or associated with
>> existing objects, rather then having TForm, TFrame etc as its sub properties
>> or components. In this way the display code is implemented directly by the
>> form or frame, rather than having the TImplementsDisplayState object
>> manipulate the form or frame's elements directly.
>> In effect is it possible to put a group of unrelated objects into the same
>> type definition by adding to them a set of identically defined functions?
>> --
>> Frank Church
>> =======================
>> http://devblog.brahmancreations.com
> I think interfaces are what I need here. I'm going to do some more reading.

Frank, reading your initial question, I think the interfaces are good for
the task, but if it's just about calling a single method or two, I'd choose
just passing/register method pointers. it's something about interfaces that
I don't like much. When I'm a user of DirectX, it's ok, it's just a
convenient way to access the API and it looks like you just use objects. But
when I implement them in my own project as a way of interation between
objects, it smells multiple inheritance, this thing I'd avoid with any
programming language.

Max Vlasov
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