Cannot use IsEmpty

[Handoko]

Code: Pascal  [Select][+][-]

1.   if Edit1.Text.IsEmpty then Exit;

Edit1 is a TEdit, but I got compile time error: "Illegal qualifier".
Why? And how to solve it?
I'm using Lazarus 1.8.0

[mrguzgog]

What about if edit1.text = '' ?

EDIT typo, sorry

[wp]

Edit1.IsEmpty ?

[WooBean]

Try this:

if string(self.Edit1.Text).IsEmpty then .... .

[Handoko]

The old-fashioned way Edit1.Text = '' works perfectly, but IsEmpty is something new in 2018.
I just want to experiment with the new writing style.

Edit1.IsEmpty causes compile time error: Error: identifier idents no member "IsEmpty"

Did I find a bug? IsEmpty is a StringHelper and the result of Edit1.Text is a string.

This one works:
if string(self.Edit1.Text).IsEmpty
But looks ugly, I rather prefer the old-fashioned way.

[WooBean]

Well, class type helper member ''IsEmpty" is for string but not for TCaption, so I wrote
"if string(self.Edit1.Text).IsEmpty ...."

[Blaazen]

@ Did I find a bug? IsEmpty is a StringHelper and the result of Edit1.Text is a string.

I don't think so. IMO it's similar reason why you cannot pass property as reference ( procedure xxxx(var ...); ) because it has no adress.
Property Text is in fact function (getter) GetText.

[Handoko]

Both the reasons are reasonable, but sad to know about that I can't use it on some cases.

[rvk]

Did I find a bug? IsEmpty is a StringHelper and the result of Edit1.Text is a string.

As already said .Text references a getter.
But that shouldn't be a problem because this works too:

Code: Pascal  [Select][+][-]

1. function Foo: String;
2. begin
3.   Result := 'Foo';
4. end;
5.  
6. procedure TForm1.Button1Click(Sender: TObject);
7. begin
8.   if Foo.IsEmpty then Exit;
9. end;

It's the fact the .Text is TCaption which is defined as "type String" (via TTranslateString).
This also doesn't work:

Code: Pascal  [Select][+][-]

1. type
2.   Foo = type String;
3.  
4. procedure TForm1.Button1Click(Sender: TObject);
5. begin
6.   if Foo.IsEmpty then Exit;
7. end;

But this works:

Code: Pascal  [Select][+][-]

1. type
2.   Foo = String;
3.  
4. procedure TForm1.Button1Click(Sender: TObject);
5. begin
6.   if Foo.IsEmpty then Exit;
7. end;

So the fact TCaption is defined as "type String" (via TTranslateString) is the problem.
If it was defined just "String" it could work.

Question is, why does it have "type" before String ??

[Xor-el]

Question is, why does it have "type" before String ??

Because type TCaption is defined as a new type not as an alias to a string.

So in simple terms, TCaption is not meant to assignment compatible to a string without some cast or some compiler magic (which it does sometimes).

[bylaardt]

Solution 1:

Code: Pascal  [Select][+][-]

1. {$MODESWITCH TYPEHELPERS}
2.  
3. type        
4.  
5.   TMyCaptionhelper = Type Helper for TCaption
6.   public
7.      function IsEmpty:boolean;
8.   end;
9.  
10. implementation
11.                                        
12. function TMyCaptionhelper.IsEmpty: Boolean;
13. begin
14.   Result:=Length(self)=0;
15. end;    
16.  

So you can use as you expected.

Solution 2:

Code: Pascal  [Select][+][-]

1.   String(edit1.text).isempty;
2.  

[Handoko]

Awesome.
I put your solution 1 into MyUtilities unit.