RFC on range design for D2

[Manfred_Nowak]

Andrei Alexandrescu wrote:

>  feedback would be highly appreciated

1) Example in "4. Bidirectional range"

Reversing of ranges can be done in constant runtime, but the example 
exposes runtime linear in the number of elements.

This might be a hint, that a "6. Reversable Range" might be required, 
because a range reversable in constant time requires more space.


2) [left,right][Diff,Union]

Ranges are not sets; therefore not only me might have problems to 
capture the idea behind "difference" and "union" on ranges.

Of course one can define whatever one wants, but I would prefer
[sub,snip,cut,split,...][B,E][B,E] (r,s)

I.e. `subBB(r,s)' is the subrange of `r' starting at the beginning of 
`r' and ending at the beginning of `s' (including the beginning of `r', 
but not including the beginning of `s').

It my be of some worth to include the `B' or `E' as parameters to the  
choosen keyword(?) to enable algorithmically accesses:

| sub(B,B,r,s)

instead of `leftDiff( r, s)'

-manfred
-- 
If life is going to exist in this Universe, then the one thing it 
cannot afford to have is a sense of proportion. (Douglas Adams)