IfThenStr does not work - omg

[paule32]

Hello,

given following Code:

Code: Pascal  [Select][+][-]

1. function IfThenStr(Condition: Boolean; TrueValue, FalseValue: String): String;
2. begin
3.   if Condition then Result := TrueValue else Result := FalseValue;
4. end;
5.  
6. function foo(AString: String): String;
7. begin
8.   result := 'bar';
9. end;

then I get Compiler Error - Boolean expected for Parameter 2 by using:

Code: Pascal  [Select][+][-]

1. checkList.Checked[1] := ifThenStr(
2.   checkList.Items[1] = foo('All Header: ON'),
3.   foo('All Header: OFF'),
4.   foo('All Header: ON')
5. );

do I something missing ?

[Ally]

Hello paule32,

Does it work if you enclose the first parameter in brackets?

Code: Pascal  [Select][+][-]

1. checkList.Checked[1] := ifThenStr((checkList.Items[1] = foo('All Header: ON')), foo('All Header: OFF'), foo('All Header: ON'));

Greetings
Roland

[wp]

Code: Pascal  [Select][+][-]

1. checkList.Checked[1] := ifThenStr(
2.   checkList.Items[1] = foo('All Header: ON'),
3.   foo('All Header: OFF'),
4.   foo('All Header: ON')
5. );

CheckList.Checked[AIndex] is a boolean property. But you assign to it a string (IfThenStr returns a string).

[paule32]

@Ally:
don't.
mainform.pas(393,28) Error: Incompatible type for arg no. 2: Got "AnsiString", expected "Boolean"

@wp:
For me, it makes no sense. Because first Parameter (1) is a Boolean.
The second (2) and third (3) Parameters are Strings.
The return Value is a String.

checkList.Items[index] is TCheckListBox.Items[index]
.Items is a TStringList.

[Nimbus]

Hi paule32,

The problem is not the function itself, but what you are trying to do with its result.
The result of the function is a String (AnsiString). And you are trying to asign it to TCheckListBox.Checked[] property, which is of Boolean type.
You can not assign a String to a Boolean, hence the error.

[paule32]

omg - blame on me...

you are right.
Checked is a Boolean

say: I am a GNU 

[cdbc]

Hi
What is GNU (G)eneral brain (N)ot (U)sed ?!? 
Regards Benny

[paule32]

yes, indeed. 100 Points !  :'(

[MarkMLl]

omg - blame on me...

you are right.
Checked is a Boolean

But at the same time, the error message isn't very helpful: at an absolute minimum you have to understand that Checked[] is a property which is implemented by something like SetChecked() with an object reference as a hidden first parameter.

Did your original error message- which you did not reproduce in full- give any useful hint in terms of line and column number?

MarkMLl

[Thaddy]

given following Code:

Code: Pascal  [Select][+][-]

1. function IfThenStr(Condition: Boolean; TrueValue, FalseValue: String): String;
2.  

You are missing that there is a generic ifthen that you can specialize to string.
I wrote that seven tears ago.

It also solves your problem.

[Thaddy]

Here's the test code I added 7 years ago:

Code: Pascal  [Select][+][-]

1. {$mode delphi}
2. uses sysutils;
3. type
4.   Ttest = function:string;
5.  
6. function SomeTestOne:string;
7. begin
8.  writestr(result,'Test1');
9. end;
10.  
11. function SomeTestTwo:string;
12. begin
13.  writestr(result,'Test2')
14. end;  
15.  
16. var
17.   a:integer = 100;
18.   b:integer = 200;
19.   c:single = 0.001;
20.   d:single = 1.000;
21.   e:TTest = SomeTestOne;
22.   f:TTest = SomeTestTwo;
23. begin
24.   writeln(ifthen<integer>(true,a,b));
25.   writeln(ifthen<integer>(false,a,b));
26.   writeln(ifthen<single>(true,c,d):2:3);
27.   writeln(ifthen<single>(false,c,d):2:3);
28.   writeln(ifthen<Ttest>(true,e,f));  // executes e
29.   writeln(ifthen<Ttest>(false,e,f)); // executes f
30.   writeln(ifthen<string>(true,'true','false'));
31.   writeln(ifthen<string>(false,'true','false'));  
32. end.

This is in 3.2.0 and higher.
In your case, look at the last 4 examples.

[MarkMLl]

You are missing that there is a generic ifthen that you can specialize to string.
I wrote that seven tears ago.

Documented where?

MarkMLl

[Thaddy]

Good point. There is documentation for it, including something close to above example, but this feature somehow did not make it to current documentation (although Michael made the actual commit).

Issue #34012, closed and commited.

(The generic randomfrom I mentioned in the comments is probably also not documented)

I guess those patches were too trivial. :'( but most of my patches made it to documentation.

[Nimbus]

I'm not sure the TS needs this advice in any way, but note there's also non-generic version in StrUtils, which has been there for ages, I believe

https://www.freepascal.org/docs-html/rtl/strutils/ifthen.html

[Thaddy]

That was already mentioned.
Note that he actually executes function parameters and does not pass simple strings. Hence the generic is actually better suited for his problem because it is not restricted to returning a string.