[fpc-devel] Interface scope incompatibility with Delphi

Michael Van Canneyt michael at freepascal.org
Wed Nov 10 11:24:52 CET 2010

On Wed, 10 Nov 2010, Graeme Geldenhuys wrote:

> Op 2010-11-10 11:56, Michael Van Canneyt het geskryf:
>> Well, the original coders made assumptions which they're not supposed to make.
> To be fair, it has worked for over a decade already. Plus many IDE and
> Compiler add-on vendors implement their products based on Delphi behaviour
> (even though it might not all be documented). The same gets done for
> Windows apps in general - working on Windows behaviour. Lets not speculate
> if it will be broken or not in the next Delphi release (nobody knows the
> answer to that, and there is no reason why it will be broken then). All I
> am saying is that in the current "released" Delphi versions (at least down
> to D7, probably D6 too) this feature works. The "mouse cursor" trick using
> the same Interface behaviour has been in tiOPF code for years, and I think
> that's where I saw it first.
> And the fact that so many developers asked about Interface scope problems
> in the past [as you mentioned], clearly indicates that that should be the
> expected behaviour in FPC too.

As soon as it becomes spec, yes. Otherwise no.

Just like the 'const is passed by ref'. No, it is not, and won't be: it's up
to the compiler's dicretion.

>> Nowhere is the Delphi behaviour guaranteed, not even by Delphi.
> Well, I can always argue that FPC tries to clone/mimic Delphi behaviour in
> many ways... it's that little FPC design goal called "delphi
> compatibility". Think of all the poor developers trying to port their
> Delphi code to FPC.  ;-)

Yes, valid and documented code is supported. 
This is invalid code which just so happens to work.

There are more cases where we are incompatible. All of them for good reason.


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