Re: [fpc-pascal] How to assign overloaded event handler?

[Michael Van Canneyt via fpc-pascal]

On Wed, 14 Sep 2022, Thomas Kurz via fpc-pascal wrote:


I don't know whether this is actually a bug or not but I cannot find a hint in 
the documentation.

It seems that methods assigned to an event handler are not allowed to be 
overloaded. Or, to be more precise, FPC always uses the first declaration 
regardless whether it fits or not.

Example:


program Project1;

uses Classes;

type TTest = class(TObject)
 procedure SomeEvent (Sender: NativeInt); overload;
 procedure SomeEvent (Sender: TObject); overload;
end;

procedure TTest.SomeEvent (Sender: TObject);
begin
end;

procedure TTest.SomeEvent (Sender: NativeInt);
begin
end;

var
 x: TTest;
 y: TStringList;

begin
 x := TTest.Create;
 y := TStringList.Create;
 y.OnChange := @x.SomeEvent;
end.



This doesn't work:

project1.lpr(25,17) Error: Incompatible types: got "" expected ""

However, when switching both SomeEvent declarations so that the "TObject" 
variant appears first, it does work.

Imho, it should considered a bug because the compiler should be able to detect 
that there is a matching overloaded method and assign that one.


This is indeed a bug.



In my simple example, the solution is, of course, to swap declarations. But I'm 
assigning event handler to a generic class and need event handlers with 
different types. And it would be helpful if they had the same name when serving 
the same purpose.

Is there a possibility to tell FPC to use a particular method in the assignment? 
Something like "OnChange:=@(TNotifyEvent(SomeEvent))"?


There is not.

Please file a bugreport so it does not get forgotten.

Michael.

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[fpc-pascal] How to assign overloaded event handler?

[Thomas Kurz via fpc-pascal]

I don't know whether this is actually a bug or not but I cannot find a hint in 
the documentation.

It seems that methods assigned to an event handler are not allowed to be 
overloaded. Or, to be more precise, FPC always uses the first declaration 
regardless whether it fits or not.

Example:


program Project1;

uses Classes;

type TTest = class(TObject)
  procedure SomeEvent (Sender: NativeInt); overload;
  procedure SomeEvent (Sender: TObject); overload;
end;

procedure TTest.SomeEvent (Sender: TObject);
begin
end;

procedure TTest.SomeEvent (Sender: NativeInt);
begin
end;

var
  x: TTest;
  y: TStringList;

begin
  x := TTest.Create;
  y := TStringList.Create;
  y.OnChange := @x.SomeEvent;
end.



This doesn't work:

project1.lpr(25,17) Error: Incompatible types: got "" expected ""

However, when switching both SomeEvent declarations so that the "TObject" 
variant appears first, it does work.

Imho, it should considered a bug because the compiler should be able to detect 
that there is a matching overloaded method and assign that one.

In my simple example, the solution is, of course, to swap declarations. But I'm 
assigning event handler to a generic class and need event handlers with 
different types. And it would be helpful if they had the same name when serving 
the same purpose.

Is there a possibility to tell FPC to use a particular method in the 
assignment? Something like "OnChange:=@(TNotifyEvent(SomeEvent))"?

Kind regards,
Thomas

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