[fpc-devel] New feature discussion: for-in loop

[Alexander Klenin]

On Thu, Oct 22, 2009 at 00:26, Michael Van Canneyt
<michael at freepascal.org> wrote:
>> I beg to disagree.This is completely backwards -- like saying that "while" loop is an
>> ugly hack to save some typing of "goto" operators.
>> Iterators and foreach loops are very important tools of structured coding.
>> The fact that "for..in" may be expressed in terms of lower-level
>> primitives
>> does not decrease its importance, just like existence of "goto" does
>> not decrease the importance of "while".
>
> Well, I think you can't compare the two cases.
>
> I see little gain in changing
>
>  while Something(f) do
>    F.Somethingelse
>
> to
>
>  For f in Something do
>    F.SomethingElse
>
> The number of lines is equal, the amount of typed characters also is equal.
> It's not more readable, either, IMHO.

I understand what this thread is very long and hard to follow.
However, could you please at least read direct the answers to your mails:

On Tue, Oct 20, 2009 at 20:25, Alexander Klenin <klenin at gmail.com> wrote:
> On Tue, Oct 20, 2009 at 20:09, Michael Van Canneyt
> <michael at freepascal.org> wrote:
>> But I really don't see the advantage of being able to type
>>
>>  For F in Someclass.Iterator do
>>    F.Something
>>
>> over
>>
>>  While SomeClass.HaveValue do
>>    SomeClasss.NextValue.Something;
>>
>> It's not clearer, at most it saves you a couple of keystrokes.
>
> This is because the while you provided is not equivalent to the for loop above.
> The correct translation would be:
> var
>  it: TSomethingIterator;
> ...
>  it := SomeClass.Iterator;
>  try
>    while it.HaveValue do
>      it.NextValue.Something;
>  finally
>    it.Free;
>  end;
>
> Now, that is quite e few keystrokes to save, not to mention that
> if item value is used more than once in the loop, SomeClass.NextValue must be
> stored in a variable, further bloating code.

There is another thing:

On Thu, Oct 22, 2009 at 00:26, Michael Van Canneyt
<michael at freepascal.org> wrote:
> When there is a big difference between the following goto and the while loop
> it is supposed to be equal to:
>
>  :jumphere;
>  If Something(F) then
>    begin
>    F.SomeThingElse;
>    Goto jumphere;
>    end;
>
> Here you need quite a few more lines and even an extra label definition, and
> I don't think anyone will dispute that the while loop is more readable...

The main advantage of "while" as compared to "if + goto" is not the code size
(there are times when using "goto" leads to shorter code),
but in the fact that it represents a more structured approach to coding,
reducing a probability of mistakes and easing code maintenance.
This is the main argument in favor of "for..in" as compared to "try +
while + manual iterator calling".

-- 
Alexander S. Klenin