[fpc-devel] for-in-index loop

[Alexander Klenin]

On Sat, Jan 26, 2013 at 10:34 PM, Michael Van Canneyt
<michael at freepascal.org> wrote:
> But if I must choose between
>
> for a,b in c do
>
> (with C a tuple enumerator/iterator) or
>
> for a in c index b do
>
> Then the former is ten times (well, a lot) better.
>
> So if someone were to introduce that to solve the original poster's problem,
> you will not hear me protesting, it will have been well worth the energy I
> put in this discussion.
>

There are two reasons I proposed latter instead of former:
1) I think using keyword is more explicit and readable
2) I thought that smaller feature is easier to argue for than a large one --
  apparently, I was mistaken on that :)

So, amended "for-in-index" proposal:
1) The syntax is
for value, key in container do ...
2) The enumerator interface is extended with optional
property CurrentWithKey: TValueKey;
where TValueKey must be a record with two fields.
This property will be called in the case of two-argument for-in,
while the case of single-argument for-in continues to work as-is
for both compatibility and efficiency.
3) When/if the full tuple proposal gets implemented, "for-in-index",
now aka "for-key-in", will became a proper subset of it.

What do you think?

--
Alexander S. Klenin