[fpc-devel] Allow record helper inheritance in Delphi mode

[Sven Barth]

Am 01.09.2017 12:15 schrieb "Maciej Izak" <hnb.code at gmail.com>:
>
> 2017-09-01 11:41 GMT+02:00 Stefan Glienke <sglienke at dsharp.org>:
>>
>> Again you will cause unnecessary headaches because now your helper has
the dependency of the builtin and the third party one.
>> How would third party one and third party two implement them? They both
probably would extend the builtin one. Which one can you use in your code
then?
>> Yes, the one that comes last in the uses. What if you want to use
functions from both? Out of luck again.
>>
>> Inheritance regardless what form is never is the best option here. I
think "ancestor list" is just a misnomer in the documentation as it cannot
be a list but only one in case of class helper.
>
>
> The control of modules order in uses section can turn programmers life
into real hell for type helpers. I think that new directive
$EXPLICITHELPERS should help :
>
> type
>   TH1 = record helper for string
>     procedure foo;
>     procedure foo1;
>   end;
>
>   TH2 = record helper for string
>     procedure foo;
>     procedure foo2;
>   end;
>
>   TH3 = record helper for string
>     procedure foo;
>     procedure foo3;
>   end;
>
> var
>   s: string;
> begin
>   s.foo; // call TH3.foo
>
> {$EXPLICITHELPERS TH1 for string} // scope for helpers limited only to TH1
>   s.foo; // call TH1.foo
>   s.foo3; // error
>
> {$EXPLICITHELPERS TH2, TH1 for string}
>   s.foo; // call TH2.foo
>   s.foo1; // call TH1.foo1
>
> {$EXPLICITHELPERS default for string}
>   s.foo; // call TH3.foo
>
> {$EXPLICITHELPERS TH1, default for string}
>   s.foo; // TH1.foo
>   s.foo1;
>   s.foo2;
>   s.foo3;
> end.

No, directives won't be abused for something like that.

Regards,
Sven
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