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

[Jonas Maebe]

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.


Jonas