[Issue 7177] $ should forward to length by default

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=7177



--- Comment #24 from Steven Schveighoffer <schveiguy at yahoo.com> 2013-03-21 10:14:53 PDT ---
(In reply to comment #22)
> Because if you don't, then you can never use $ when slicing a range.

This is extreme.  You certainly CAN use $ with ranges that support $.

> And really, isRandomAccessRange should require that $ work with finite ranges for
> the same reason. As it stands, you pretty much can't use $ in generic code.
> It's only good for arrays, because you can't count on it working for anything
> else.

Yes you can, it just requires the range supports $.  Define supportsDollar
trait.  Done.

> The appropriate range templates must be able to require them for us to be
> able to use them, and if we change them to require opDollar without this
> enhancement request, then it's going to break a lot of code.

Then don't change them.  Requiring $ is as simple as defining a trait that
checks for $ support.  There is no reason slicing has to be predicated on
having an end point.  And having an end point does not require having a length
(see strings) and is not necessarily an integer value equivalent to the length.

If, for example, we add requiring $ for isRandomAccessRange, and then have a
function that requires a random access range but doesn't use $, what is the
benefit of doing that?  Either you need $ or you don't, and that is
quantifiable with a separate trait.  Support for slicing or indexing is a
precondition for having $ but $ is not required in order to slice or index.

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