RFC on range design for D2

[Andrei Alexandrescu]

Sean Kelly wrote:
> Andrei Alexandrescu wrote:
> ...
>>
>> After much thought and discussions among Walter, Bartosz and myself, I 
>> defined a range design and reimplemented all of std.algorithm and much 
>> of std.stdio in terms of ranges alone.
> 
> Yup.  This is why I implemented all of Tango's algorithms specifically 
> for arrays from the start--slices represent a reasonable approximation 
> of ranges, and this seems far preferable to the iterator approach of 
> C++.  Glad to hear that this is what you've decided as well.

That's great to hear, but I should warn you that moving from arrays to 
"the lowest range that will do" is not quite easy. Think of std::rotate 
for example.

>> This is quite a thorough test because the algorithms are diverse and 
>> stress-test the expressiveness and efficiency of the range design. 
>> Along the way I made the interesting realization that certain 
>> union/difference operations are needed as primitives for ranges. There 
>> are also a few bugs in the compiler and some needed language 
>> enhancements (e.g. returning a reference from a function); Walter is 
>> committed to implement them.
> 
> Very nice.  The inability to return a reference has been a thorn in my 
> side for ages.
> 
>> I put together a short document for the range design. I definitely 
>> missed about a million things and have been imprecise about another 
>> million, so feedback would be highly appreciated. See:
>>
>> http://ssli.ee.washington.edu/~aalexand/d/tmp/std_range.html
> 
> It seems workable from a 1000' view.  I'll have to try and apply the 
> approach to some algorithms and see if anything comes up.  So far, 
> dealing with bidirectional ranges seems a bit weird, but that's likely 
> more related to the syntax (ie. 'pop') than anything.
> 
> 
> Sean
> 
> P.S. This decision has interesting implications for D2+, given the 
> functional tendencies already present in the language :-)

Wait until you see the generators! An efficient generator of Fibonacci 
numbers in one line...

auto fib = generate!("a[0] + a[1]")(1, 1);

I'm so excited I can hardly stand myself. :o)


Andrei