Iterators for D

[Bill Baxter]

Walter Bright wrote:
> Knud Sørensen wrote:
>> On Mon, 06 Nov 2006 12:46:01 -0800, Walter Bright wrote:
>>
>>> It's becoming increasingly obvious that D needs iterators. While 
>>> opApply   is far better for some kinds of iteration (such as 
>>> recursively traversing a directory), iterators are more efficient in 
>>> some cases, and allow for things that opApply makes difficult.
>>>
>>
>> What are those cases ? Maybe we can find a way to fix the problem with
>> opApply.
> 
> One such case is the usefulness of being able to provide an input 
> iterator to a parsing function, which may itself pass the iterator off 
> to other parsing functions.

Another case is the desire to iterate over multiple containers at the 
same time, say as you would do in a sorted list merge operation. 
opApply could handle this one if D had real coroutines (i.e. multiple 
opApply's could be running simultaneously)

Another case is the basic desire to hold onto a pointer to a container 
for later use.  For instance if you have an STL style linked list 
container where the implementation (the actual nodes) are hidden from 
the user.  You still want the user to be able to keep something that 
functions like a pointer to a particular insertion point in the list 
(and be able to use that in generic sequence manipulation algorithms).

--bb