[fpc-pascal] private integer is an illegal counter variable

Jonas Maebe jonas.maebe at elis.ugent.be
Fri Nov 27 15:56:21 CET 2009

On 27 Nov 2009, at 15:49, Juha Manninen wrote:

> If I define a private integer:
>  TDemo = class(TCustomApplication)
>  private
>    i: integer;
>    ...
> and in a protected method I use it:
>  for i := 0 to List.Count - 1 do
>    ...
> then I get an error:
>  Error: Illegal counter variable
> Moving it to method's var section helps.
> Method's var section is also better place for it in general, but  
> still it
> should be legal to use a private member as counter var.

The reason is that a for-loop tries to make a number of reasonable  
guarantees that the counter variable cannot be modified during the  
loop. E.g., direct assignments to a counter variable are forbidden  
inside the loop (except in TP-mode). If you use a private field, then  
any method of that class called in the body of the loop can easily  
(accidentally) change the value of the counter variable, completely  
messing up the loop.


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