Awesome paper; everybody should read it ;-)
Collections aren't necessarily about fundamentally linear structures,
but about *linearizable* structures. If you want to build a system of
generic algorithms that work efficiently on all kinds of data
structures, flat linearity won't always be the most efficient
abstraction, but:
1. It's generally simpler to write linear algorithms (e.g. even copying
from one hierarchical data structure to another with different
intermediate segment boundaries can be hard to code).
2. You'll want the linear specialization for the leaves of your data
structure regardless of what else you do, so having a linearized
abstraction is important even if you're going to build a hierarchical
one.
···
on Thu Mar 03 2016, Dmitri Gribenko <swift-evolution@swift.org> wrote:
On Thu, Mar 3, 2016 at 9:56 AM, plx via swift-evolution > <swift-evolution@swift.org> wrote:
# General Remarks: Great!
Thanks for sharing this proposal; it's a big change, but will be a
big improvement once it's in place, and it's encouraging to see the
team is willing to undertake changes of such scale.I'm not sure how much discussion you'll actually manage to scare up
b/c the issues this proposal addresses are *not* common, but are
nevertheless rather significant when encountered.E.G.: it's nice to be able to create simple
chain/product/etc. collection-combinators which can, themselves, be
collections, without winding up with indices indices forced to
choose between *either* holding a back-reference to retrieve various
startIndex/endIndex values as-needed *or* carrying around a complete
set of all needed startIndex/endIndex values.Agreed! We already have that problem in the lazy flatMap collection.
I don’t have any negative feedback that isn’t subsumed by the next section.
# Concern: Linearity Baked-In
Even with this change, I have some concern that the proposed
protocol hierarchy from `Collection` onward feels like it has a
foreseeable lack of generality due to how strongly "linear" the
design wants `Collection` to be.Is this the right time to raise such concerns (e.g. in-scope for this discussion)?
We can definitely dive into more details about this. One thing that I
would want to understand is whether this non-linearity concept could
be added later without a re-design.Could you provide more information about the linearity issues that you
have in mind? Are you thinking of something like Segmented Iterators
and Hierarchical Algorithms [1]?
--
-Dave