[fpc-devel] Local procedures as procedural parameter

[olle.r at automagika.se]

>>> Procedure iso_fun( function f( x: real): real);>>> begin
>>>   StoredF:=F;
>>> end;
>>
>> This assignment is invalid, it's the same as trying to assign a method
>> to a
>> regular procedural variable.
>
> This is exactly my point: how does the compiler distinguish the two in
> this case ?

Possible soultions: They have different datatypes, or a flag is set in the
type definition.

> I don't see how, unless you add an extra parameter for the 'iso' way of
> doing things.
>
> So, basically, to be able to use a local procedure as a callback,
> - You must declare a function with the ISO way to specify a callback.
> - This function is not usable with a global callback function.
> -> So if you would want to use such a function for both normal and local
>    procedures, you would have to implement it twice !
>
> If this is indeed the case, then it is totally ridiculous in my opinion
> to implement such a "feature", because if you must make special amends
> _anyway_, then you can just as well do it with global functions, without
> the local variants.
>
> I would only see the use of being able to pass a local function as a
> callback
> if the called function can be used for both local and global callback
> procedures.

It can. When a global proc is passed, the static link is set to nil.

> I question the usefullness of this whole "feature".

When using a call back, you dont need to pass data to it as global
variables, making code cleaner.

Olle