Hello,

Following the bug discovered in the class variables (on fpc devel), I actually would like to know the need (or usage) for variables and class variables in a class (I know it's a delphi thingy, but still).

Furthermore, why can't I create a class field, so the field will have the same value on each instance of the class and it's sub classes ?

Thanks,
Ido

LINESIP websites:
http://www.linesip.com
http://www.linesip.co.il

Hello FPC-Pascal,

Friday, November 5, 2010, 8:54:08 PM, you wrote:

i> Following the bug discovered in the class variables (on fpc devel), I i> actually would like to know the need (or usage) for variables and class i> variables in a class (I know it's a delphi thingy, but still). i> Furthermore, why can't I create a class field, so the field will have the i> same value on each instance of the class and it's sub classes ?

As far as I know, scope. Example:

TClass1=class
public
  var class count: integer;
  Constructor Create;
end;
constructor TClass1.Create;
begin
  inc (Count);
end;
function How(): integer;
begin
  Result:=TClass1.Count;
end;

------------------------------------

TClass1=class
public
  Constructor Create;
end;
var
  TClass1_Count: integer=0;
constructor TClass1.Create;
begin
  inc (TClass1_Count);
end;
function How(): integer;
begin
  Result:=TClass1_Count;
end;

--------------------------------------

I think both are basically identical, but the work of the first one is much more clear. I had never used them, but I think the above code is right, do not ?

I think both are basically identical, but the work of the first one is much more clear. I had never used them, but I think the above code is right, do not ?

Yes. Usually we need this when creating a thread pool, so we know how many threads have been created.

But why class variables and not class fields ?

Ido

LINESIP websites:
http://www.linesip.com
http://www.linesip.co.il

ik wrote

But why class variables and not class fields ?

As I personally think about normal class fields as "variables per class instance", I see no difference between calling something "class field" or "class variable".

If it is the "var" keyword you are stumbling on, then let me tell you that normal fields can also be started with "var" (which is needed when you defined class types or constants before that).

E.g. (compiled with 2.5.1):

   TTest = class
   private
     const
       Foo = 42;
     var
       fTestField: Integer;
   public
     property TestField: Integer read fTestField;
   end;

Regards,
Sven

ik wrote

But why class variables and not class fields ?

What is the difference?

"var" is already a reserved word. reserving a word "field" will cause more problems than using an already reserved word.

Best regards,
Paul Ishenin.

why not something like this:

TAClass = class
private
  FField : class integer;
end;

Further more, what is the difference between a "normal" field and a variable inside a class:

TAClass = class
private
  var Variable : Integer;
end;

That's what I'm trying to figure out.

Ido

"var" and "class var" starts new sections in the class declaration. Therefore you can define several class fields or instance fields after them.

For example
TAClass = class
private
   class var
     Field1: Integer;
     Field2: String;
   var
     Field3: Integer;
     Field4: String;
end;

var - you start a fields section
Variable : Integer; - you declare a field inside this section.

You can skip "var" in this case. But if you previosly had "const" or "type" section or had a method/property declaration and want to declare a field again then you need to explicitly start a field section by "var" keyword.

For example:

TAClass = class
private
   type
      TMyInt = type integer;
   var // this keyword is required here
     Field1: TMyInt;
end;

Best regards,
Paul Ishenin.

ik wrote

Further more, what is the difference between a "normal" field and a variable inside a class:

Nothing. Everything defined in a "var" section is a field. The reason the "var" keyword can now be used, is because it is now also possible to define types and constants inside classes, so you need a way to switch to defining fields after a "type" or "const" section.

Jonas