"the last change" for ranges

[Andrei Alexandrescu]

dsimcha wrote:
> Please, please, please PLEASE, PRETTY PLEASE FOR THE LOVE OF GOD ALMIGHTY tell me
> you're not serious!!!  Isn't changing the interface such that forward ranges are
> no longer effectively a subtype of input ranges a bit drastic?  Or do you have
> some magic up your sleeve that, given any forward range, will automatically call
> popFront, and then front, when popNext is called, using extension function hacks
> or something?

Consider:

struct R
{
     bool empty();
     ref int front();
     void popFront();
}

ref int popNext(ref R fwdRange)
{
     auto result = & fwdRange.front();
     fwdRange.popFront;
     return *result;
}

void main()
{
     R r;
     int x = r.popNext;
}

This should work, I just noticed with surprise it doesn't. It's a bug, 
specifically bug 3015:

http://d.puremagic.com/issues/show_bug.cgi?id=3015

> The whole beauty of ranges is that they provide one standard interface to program
> to if all you need is a lowest common denominator level of functionality.
> Frankly, if you destroy this, I think that just enforcing forward vs. input ranges
> purely by convention would be the lesser of two evils.

You and I see eye to eye.


Andrei