Monthly Archives: February 2012

Functional programming style in Delphi

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Functional programming paradigm gradually finds its way even in Delphi – an imperative language without a garbage collector. Consider the next code sample that changes a button’s caption using extended RTTI (requires Delphi 2010 and above):

procedure TForm1.Button1Click(Sender: TObject);
var
  Ctx: TRttiContext;
  P: TRttiProperty;
  T: TRttiType;

begin
  T:= Ctx.GetType(TButton);
  P:= T.GetProperty('Caption');
  P.SetValue(Button1, 'RTTI');
end;

When analyzing the above code snippet note the following:

  • TRttiContext is a record type; you need not create and destroy a variable of a record type
  • TRttiProperty and TRttiType types are classes; the instances of these classes are created by correspondent TRttiType and TRttiContext methods, but you should not destroy these instances yourself – the underlying extended RTTI implementation takes care about it

As a result the above code snippet can be rewritten in a functional style:

procedure TForm1.Button1Click(Sender: TObject);
begin
  TRttiContext.Create.GetType(TButton).GetProperty('Caption').SetValue(Button1, 'RTTI');
end;

All variables have gone. No memory leaks. Does your brain hurt?