RFC on range design for D2

[Sean Kelly]

Sergey Gromov wrote:
> 
> Now the same algorithm in ranges:
> 
>> Merge_backward(R1, R2, R3)(R1 s1, R2 s2, R3 dst)
>> {
>>     for (;;)
>>     {
>>         if (s1.isEmpty())
>>             dst[] = s2[];
>>         else if (s2.isEmpty())
>>             dst[] = s1[];

I'm not sure the above is correct.  It should return after the copy is 
performed, and the code also assumes that the size of dst is equal to 
the size of s2 and s1, respectively.

>>         else if (s1.last < s2.last)
>>         {
>>             dst.last = s1.last;
>>             s1.shrink();
>>         }
>>         else
>>         {
>>             dst.last = s2.last;
>>             s2.shrink();
>>         }
>>         dst.shrink();
>>     }
>> }
> 
> If there were shrink-on-read and (eureka!) shrink-on-write operations, 
> it would be even shorter:
> 
>>         else if (s1.last < s2.last)
>>             dst.putBack(s1.getBack());
>>         else
>>             dst.putBack(s2.getBack());
> 
> where both getBack() and putBack() shrink the range from the end side.

Very slick.


Sean