Revised RFC on range design for D2

[Benji Smith]

Andrei Alexandrescu wrote:
> In wake of the many excellent comments and suggestions made here, I made 
> one more pass through the draft proposal for ranges.
> 
> http://ssli.ee.washington.edu/~aalexand/d/tmp/std_range.html
> 
> There are some comments in red illustrating some uncertainties (not 
> all), and the names of the primitives have been updated. Bicycle shed 
> galore! But don't forget to comment on the reactor as well :o).

Well done. I think the design has come together very nicely. I'm 
especially happy with all the new names, which make a big difference for 
me in being able to visualize how the proposal works. The old names 
(fromLeft, etc) were very opaque to me.

(btw: head & toe? i love it!)

In its current state, this actually gets me pretty excited about D2. 
Maybe even enough to finally slog my way through all the const stuff.

One tiny typo, though: In the "Forward range" section, the code sample 
still uses "left" instead of "head".

And, there are two sections (which I think are related to one another) 
that left me scratching my head:

Input Ranges:
"In case ElementType!(R) has aliases (such as a reference, pointer, or 
array type), the iterator is free to recycle it it upon the call to 
r.next, so client code must do a deep copy if preserving the value is 
needed. [NOTE: This is a weakness in the design. A better way of 
figuring recycling should be found.] The call is defined only right 
after r.done returned false."

Forward Ranges:
"Also, forward ranges iterate over "real" elements, which makes in-place 
mutation of r.head possible."

Those paragraphs are completely greek to me. Can you elaborate?

--benji