Today I learned... :)

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Today I learned... :)
I didn't know about this syntax for properties:

    FStrings: array [0..1] of string;
    property String0: string read FStrings[0] write FStrings[0];
    property String1: string read FStrings[1] write FStrings[1];

Comments

  1. Igor SchevchenkoApril 21, 2014 at 4:16 AM

    What the version of Delphi ?

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  2. Roman YankovskyApril 21, 2014 at 4:29 AM

    Igor Schevchenko I tried this in Delphi 7

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  3. Alex EgorovApril 21, 2014 at 4:48 AM

    Very interesting...

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  4. Igor SchevchenkoApril 21, 2014 at 5:42 AM

    Roman Yankovsky Wow! Haven't seen this too :)

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  5. Daniela OsterhagenApril 21, 2014 at 7:29 AM

    Works in Delphi 6 too. I haven't got anything older here to test it.

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  6. Daniela OsterhagenApril 21, 2014 at 7:44 AM

    Delphi 5 too, I just found my old notebook that still had it installed.

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  7. Евгений СавинApril 21, 2014 at 11:39 AM

    Well, may be somebody dont know:
    FRec: TMyRecord;
    property Prop: Integer read FRec.IntField;

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  8. Daniela OsterhagenApril 21, 2014 at 1:41 PM

    Евгений Савин That one only works read only, iirc

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  9. Arioch TheApril 21, 2014 at 6:06 PM

    Nothing special, as long as you go with statically allocated variables. Same as

    Private FStrings : record v0,v1: string end;
    Public property string1: string read FStrings.v1;

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  10. Arioch TheApril 21, 2014 at 6:08 PM

    Daniela Osterhagen in new version. In old versions you could assign part of the records. That was handy but conceptually was a bug and later they fixed the hole.

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  11. Евгений СавинApril 21, 2014 at 11:09 PM

    Daniela Osterhagen  you CAN use 'write'
    type
      TMyObj = class
      private
        FRec: record Str: string end;
      public
        property StrProp: string read fRec.Str write FRec.Str;
      end;

    Arioch The 
    No, no. You say about other bug

    TMyObj2 = class
    private
      function GetRec: TRec; // TRec is record
    public
      property Prop: TRec read GetRec;
    end;

    O := TMyObj2.Create;
    O.Prop.RecordField := 10; // there was bug in old delphis, but not now

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  12. Igor SchevchenkoApril 22, 2014 at 1:51 AM

    The features are interesting, but I guess, its usage increases overall code unreadability. IMO.

    Евгений Савин  Still can't assign to particular fields of record property (XE5).

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  13. Eric GrangeApril 22, 2014 at 1:58 AM

    > O.Prop.RecordField := 10; // there was bug in old delphis, but not now

    I'm actually not sure accepting that isn't a bug (as if the compiler accepts it, it means you can't have read-only record properties)

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  14. Евгений СавинApril 22, 2014 at 3:11 AM

    Igor Schevchenko 
    >>Still can't assign to particular fields of record property (XE5). 
    But in delphi 2007 or delphi 2010(i dont remember when this bug was fixed) you can.

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  15. Igor SchevchenkoApril 22, 2014 at 3:30 AM

    Евгений Савин I meant:

    unit main;

    interface

    uses
      Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
      Dialogs;

    type
      TFoo = record
        Bar1: Integer;
        Bar2: string;
      end;

      TForm1 = class(TForm)
        procedure FormCreate(Sender: TObject);
      private
        FFoo: TFoo;
      public
        property Foo: TFoo read FFoo write FFoo;
      end;

    var
      Form1: TForm1;

    implementation

    {$R *.dfm}

    //2006 [Pascal Error] main.pas(32): E2064 Left side cannot be assigned to
    //XE2 [DCC Error] main.pas(33): E2064 Left side cannot be assigned to
    procedure TForm1.FormCreate(Sender: TObject);
    begin
      Foo.Bar1 := 1;
    end;

    end.

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  16. Евгений СавинApril 22, 2014 at 5:41 AM

    I found ref to related bug http://stackoverflow.com/questions/1920140/delphi-records-in-classes (in XE4 or may be earlier fixed)  
    Well, I think it's not very important now.

    ReplyDelete

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