Generics - ancestor class and virtual method override
lazarus / 62-General

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korba812 · 2022-02-13 15:44

I just discovered a new (for me) functionality for generic classes:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i type  TFoo
= class    function DoFoo: Integer; virtual;  end;   generic TBar<T:
TFoo> = class(T)    function DoFoo: Integer; override; // <- Error:
There is no method in an ancestor class to be overridden:
"DoFoo:LongInt;"    function DoBar: Integer; virtual; 
end; Unfortunately, there is no way to override virtual methods in
this way. Is such a possibility planned?

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Thaddy · 2022-02-13 18:59

Of course not! That is programmer error.

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korba812 · 2022-02-13 19:33

It's a pity because it looks pretty useful.

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Martin_fr · 2022-02-13 19:44

There is an open bug
https://gitlab.com/freepascal.org/fpc/source/-/issues/36843

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korba812 · 2022-02-13 19:57

So where is the bug - whether the compiler allows to create such a
generic class or that the compiler does not find virtual method in the
ancestor class?

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Martin_fr · 2022-02-13 20:02

Quote from: korba812 on February 13, 2022, 08:57:10 pmSo where is the
bug - whether the compiler allows to create such a generic class or
that the compiler does not find virtual method in the ancestor class?
Well there is no answer from the fpc team yet. I personally would
expect that the override should work....

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korba812 · 2022-02-13 20:29

Of course. Even in its present form, it is a very useful
functionality.