'in' for plain arrays?

[Ali Çehreli]

spir wrote:
 > On Thu, 02 Dec 2010 08:54:43 -0800
 > Ali Çehreli <acehreli at yahoo.com> wrote:
 >
 >> bearophile wrote:
 >>  > Pelle M.:
 >>  >
 >>  >> It doesn't exist for performance reasons, I think.
 >>  >
 >>  > It's not a matter of performance. Walter thinks that "in" on
 >>  > AAs searches on keys. And the "keys" of a dynamic array are its
 >>  > indices. And searching for indices in a dynamic array is not so
 >>  > useful. Therefore no "in" for dynamic/static arrays. I think
 >>  > this line of thought is not practical, and Python gets this
 >>  > better.
 >>
 >> I think Walter's is a good point. If 'in' searches among keys for AAs;
 >> for arrays, it would be implemented trivially as
 >>
 >>      (index >= 0) && (index < array_length)
 >
 > That's not the point...
 >
 >> I think that expression allows for negative index values too. And 
yes, I
 >> had to check before posting as I can't be sure about the integer
 >> promotion rules. :)
 >>
 >> If 'in' were to search among the values of arrays, then it wouldn't 
have
 >> the same meaning with AAs.
 >

 > Yes-no. In an ordered set (read: many uses of arrays),

I disagree with that. Arrays are for consecutive elements, usually 
unordered. The index is their position in the collection.

 > elements
 > conceptually are their own keys. We must have a simple way to
 > express membership test -- even if possibly costly for large
 > arrays. Else, we need a builtin Set type to do the job. (I have
 > one prototype in stock, if interesting for Phobos).

Agreed but that's a completely different data structure. Sets cannot 
satisfy the O(1) operations of arrays.

I was responding related to D's arrays, which are not sets.

Ali