Repost: make foreach(i, a; range) "just work"

[Marc Schütz" <schuetzm at gmx.net>]

IMO, any change needs to be both backwards-compatible (i.e., it 
should not only "just work", as you phrased, but existing code 
should "just keep working"), and forward-compatible, so as not to 
obstruct any potential improvements of tuple handling.

Scheme #1 fails backwards-compatibility.

Scheme #2 doesn't, but I feel the matching rules if a type is 
specified are too complicated. Instead, I would suggest just to 
always assign the variables from the right, i.e. you cannot skip 
variables, and if you specify a type, it must match the type of 
the value in this position.

If you really want to skip a tuple member (in order to avoid an 
expensive copy), a special token "_" or "$" could be introduced, 
as has also been suggested in one the tuple unpacking/pattern 
matching DIPs, IIRC.

As for unpacking a tuple value (or key), an additional pair of 
parentheses can be used, so such a feature would still be 
possible in the future:

foreach(i, k, (a,b,c); ...)

(Scheme #3 seems just too complicated for my taste. It's 
important to be intuitively understandable and predictable.)