Set of Char versus String - Error Illegal qualifier
lazarus / 61-Beginners

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rc.1990 · 2016-09-28 17:07

I am using Lazarus 1.6.0 ad FPC 3.0.0.

How can I pass the value of a Set of Char to a String?

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Compile Project, Target:
C:\Users\test\AppData\Local\Temp\project1.exe: Exit code 1, Errors: 2
unit1.pas(39,29) Error: Illegal qualifier
unit1.pas(41,44) Error: Illegal qualifier
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Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button1Click(Sender: TObject);const  TestArray = ['0'..'9',
'a'..'z', 'A'..'Z']; var  OneCharacter: string;begin  OneCharacter :=
TestArray[20];  ShowMessage('OneCharacter: ' + OneCharacter); 
ShowMessage('OneCharacter: ' + TestArray[25]);end;

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Leledumbo · 2016-09-28 17:22

Set is not an array, it's not indexable. Set is not a string, though
it can be stringified to display its current content, it's not type
compatible with string. Set is a set, you can include/exclude elements
from it, check whether certain element is part of it and operate it
with another set, but none of the operation deals with string. So you
better explain more in details what you expect from the code you
write.

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Xor-el · 2016-09-28 17:25

iterate through the set using a "for in " loop and append each value
to a string.

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rc.1990 · 2016-09-28 17:30

Thanks Xor-el and Leledumbo.

How can I stringify a set of char to display all its content into a
for loop so I can create an array of string containing all digits
0..9, small letters a..z and capital letters A..Z?

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Xor-el · 2016-09-28 18:05

// I modified your code a little to convert the set to string.
// posted this from my phone so it might not be well formatted.

procedure TForm1 . Button1Click ( Sender: TObject );
 const
 TestArray = ['0' .. '9' , 'a' .. 'z' , 'A' .. 'Z' ] ;

 var
 OneCharacter, res: string;
  C: char;
 begin
res := '';
 for C in TestArray do
begin
res := res + C;
end;
OneCharacter := res[20];

 ShowMessage ( 'OneCharacter: ' + OneCharacter);
 ShowMessage ( 'OneCharacter: ' + res[25]) ;
 end ;

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rc.1990 · 2016-09-28 18:19

Thanks Xor-el. Your solution solved my problem.

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Handoko · 2016-09-28 18:31

Xor-el is brilliant. 

What I don't understand why should we want to force set to be
compatible with char. As Leledumbo said set is not array, not string
and not type compatible with string. Although the name "set of char",
but it is not char too. I would consider set is a kind of list of
on/off (or bool).

One of the benefit of OP's code I can think of is make you type less:

Code: [Select]TestArray = ['0'..'9', 'a'..'z', 'A'..'Z'];

// vs

CharsList = '0123456789'+
            'abcdefghijklmnoqrstuvwxyz'+
            'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
But if the reason to make you type less, I would suggest my code which
is less typing compare to Xor-el's code, more exactly, easier to read
and understand:
Code: [Select]procedure TForm1.Button1Click(Sender: TObject);
const
  CharsList = '0123456789'+
              'abcdefghijklmnoqrstuvwxyz'+
              'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
begin
  ShowMessage('Char 25th = ' + CharsList[25]);
end;
Also, I want to add. The name "TestArray" is not correct. Actually
that is a set not an array.

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Handoko · 2016-09-28 18:51

Use the right tool for the job, is what I want to say.

I ever saw a youtube video, someone using Iphone to hit a nail. Of
course, you can if you want. But it will be much better to use a
hammer, right?

Thaddy ever said the benefit of using set recently (or some weeks
ago). That is for faster processing, because set is optimized for
speed and code size. It is explained on the documentation too:
http://www.freepascal.org/docs-html/3.0.0/ref/refsu17.html

But forcing set to char, you will lose all the benefits.