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

Frank Peelo f26p at eircom.net
Fri Nov 27 22:52:30 CET 2009

Jonas Maebe wrote:
> 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.

In any case, why would one want a loop counter to have any more than the 
minimum possible scope? Why would one want it to be a class data member 
at all? Surely it would be far better/neater/more elegant, if it is used 
by methods, to pass it as a parameter?


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