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

[Maciej Izak]

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.

-- 
Best regards,
Maciej Izak
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