IfThen Oddity...

[Steve Maughan 26]

The following code causes an AV:

type

  TFoo = class
  private
    fName: string;
  public
    property Name: string read fName write fName;
  end;

  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

uses
  StrUtils;

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
var
  Foo: TFoo;
begin
  Foo := nil;
  Form1.Caption := IfThen(assigned(Foo), Foo.Name, '');
end;

The line that cause the AV is the one with the "IfThen" statement. I would have thought this would set the Caption to '' if Foo was not assigned but instead I get an AV. This implies both the True and False expressions are evaluated but I can't see why. Am I missing something obvious? The project is attached. 

 

Delphi 11.1

 

Any insights appreciated. 

 

Steve

IfThenAV.zip

[Der schöne Günther 316]

Function arguments are always evaluated, then passed into the function. This "IfThen" (which I have never seen before), is just a regular function. The compiler has no knowledge that there is no need to evaluate the other arguments if the first one results to False.

[Steve Maughan 26]

3 minutes ago, Der schöne Günther said:

Function arguments are always evaluated, then passed into the function. This "IfThen" (which I have never seen before), is just a regular function. The compiler has no knowledge that there is no need to evaluate the other arguments if the first one results to False.

That makes sense. I learn something new every day!

 

Thanks,

 

Steve

[Stano 143]

I've never seen it either. Note, there is also System.Math.IfThen

[David Heffernan 2345]

IfThen as a function sucks big time. Why can't we have a conditional operator? 

[Stefan Glienke 2006]

On 8/16/2022 at 7:18 PM, David Heffernan said:

Why can't we have a conditional operator? 

Because that is not pascal-ish! /s 🙄

P.S. Yes I know about proposals to make it look pascal-ish - I even think we discussed that in another thread already.

[Alexander Elagin 143]

Oxygene from RemObjects makes it look pascalish enough:

 

var lDescriptiveText := if x < 10 then 'less than ten' else 'ten or more';

 

https://docs.elementscompiler.com/Oxygene/Expressions/If/