Inherited on Properties and co.

[Attila Kovacs 629]

Since when does inherited work on properties?  "Inherited Data". And where else except the obvious? Documentation?

I was annoyed that I could not set FData as it is private so I gave him an "inherited" in anger and fury and the compiler wasn't complaining. 😮

 

  TTreeNodeHelper = class helper for TTreeNode
  private
    function GetNodeData: TNodeData;
    procedure SetNodeData(const Value: TNodeData);
  public
    property Data: TNodeData read GetNodeData write SetNodeData;
  end;

function TVariantenTreeNodeHelper.GetNodeData: TNodeData;
begin
  Result := inherited Data;
end;

procedure TVariantenTreeNodeHelper.SetNodeData(const Value: TNodeData);
begin
  inherited Data := Value;
end;

 

Edited February 8, 2021 by Attila Kovacs

[Lars Fosdal 1792]

That is interesting - and a little disturbing.

[Uwe Raabe 2057]

48 minutes ago, Attila Kovacs said:

Since when does inherited work on properties? 

At least since Delphi 7 (cannot check versions below in the moment). Just have a look at DB.pas (out of many others):

function TFieldDefs.GetFieldDef(Index: Integer): TFieldDef;
begin
  Result := TFieldDef(inherited Items[Index]);
end;

or the ancient Contnrs.pas:

function TObjectList.GetItem(Index: Integer): TObject;
begin
  Result := inherited Items[Index];
end;

 

[Attila Kovacs 629]

@Uwe Raabe Wow. Will turn out it's on the first page of the help 🙂

[Anders Melander 1783]

57 minutes ago, Attila Kovacs said:

Since when does inherited work on properties?

Delphi 1

[Alexander Elagin 143]

From the very beginning, i.e Delphi 1. What's the problem?

[Attila Kovacs 629]

31 minutes ago, Alexander Elagin said:

From the very beginning, i.e Delphi 1.

Thx.

 

31 minutes ago, Alexander Elagin said:

What's the problem?

The gas prices. 😉

[Lars Fosdal 1792]

14 hours ago, Alexander Elagin said:

From the very beginning, i.e Delphi 1. What's the problem?

I guess private is not private - unless strict private?

[Uwe Raabe 2057]

3 minutes ago, Lars Fosdal said:

I guess private is not private - unless strict private?

FData is private, but the helper sets inherited Data, which is public.

[Lars Fosdal 1792]

If it is public, why do you need to use inherited?

I think the point just wooshed over my head here.

(Not the first time)

[Attila Kovacs 629]

@Lars Fosdal In this case I'm overriding the Data property, so this is the only way to set/get them.

[Alexander Elagin 143]

 

20 minutes ago, Lars Fosdal said:

If it is public, why do you need to use inherited?

Because Data property is re-introduced with a new signature, thus it is necessary to explicitly use the inherited property and not the new one.

[Lars Fosdal 1792]

Ah - Brain fog cleared.

Thanks, guys.

[Alexander Elagin 143]

In fact, this was a pretty common trick when implementing ccustom lists before generics.