Tuple assignment

[Brad Roberts]

On 10/6/2010 11:58 PM, Walter Bright wrote:
> Russel Winder wrote:
>> Python may be the best base to compare things to as tuple assignment has
>> been in there for years.
>>
>> Pythons choice is not a car/cdr approach but an exact match approach.
>> so if t represents a tuple datum or a function returning a tuple:
>>
>>         x = t
>>
>> then x is a tuple -- remembering that variables are all just references
>> to objects implemented via keys in a dictionary, and:
>>
>>         a , b , c = t
>> or
>>         ( a , b , c ) = t
>>
>> is tuple assignment where now t is required to be a tuple of length 3.
>> cf.
> 
> The first thought was to make it an exact match approach. Andrei thought that
> the car/cdr one was better, though, and I find it intuitively appealing, too.
> Perhaps Python missed an important use case?
> 
> Or perhaps the ambiguity as to whether the last item gets to be a value or
> another tuple is too much.

I think the ambiguity should be avoided.  There was one language I used ages ago
that used a token to signal the use of the last arg as a 'rest' usage.  If I
remember right, it used:

  (a, @b) = aggregate; // a = aggregate[0], b = aggregate[1..$]

It also allowed: (a, @aggregate) = aggregate; // essentially a pop operation.

That said, it was a weakly typed language, so it's application to D has to be
taken with an appropriate dose of salt.  For D, I think using the @ would clash
badly with the attribute syntax, so an alternative that's not horrid:

   (a, b...) = aggregate;

Later,
Brad