[swift-evolution] Checking in; more thoughts on arrays and variadic generics
razielim at gmail.com
Fri Jan 27 18:55:53 CST 2017
> On 27 Jan 2017, at 22:25, Slava Pestov <spestov at apple.com> wrote:
>> On Jan 27, 2017, at 11:44 AM, Karl Wagner via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> So, 2 quick points:
>> 1) I have often wanted a shorthand for expressing long tuples; I definitely think that’s something worth bike-shedding, e.g. - (String * 4, Int32 * 4) or something
> Why not define a struct, or a tuple consisting of two arrays?
Because I want a fixed-length guarantee; ([String], [Int]) could have any number of Strings or Ints.
It’s just a shorthand for defining long or complex tuples; we currently import C arrays as massive tuples which can be basically impossible to read.
>> 2) Having a special non-growing array type which is called “array” and separate from Array<T> is not such a good idea IMO. I would rather allow tuples to conform to protocols (see: https://github.com/apple/swift/blob/master/docs/GenericsManifesto.md#extensions-of-structural-types <https://github.com/apple/swift/blob/master/docs/GenericsManifesto.md#extensions-of-structural-types>).
>> If tuples could conform to protocols, we could say “any tuple of homogenous elements is a Collection”. There would be benefits for the standard library, too - EmptyCollection<T> would disappear, replaced with the empty tuple (),
> This sounds too clever.
Yeah… the cleverness is one of things I like about it. We get to remove these canned conformances and reduce the stdlib surface area while gaining an efficient way to express a fixed-size Collection. It would come with all kinds of supplementary benefits, such as iterating and mapping the elements of a tuple.
>> as would CollectionOfOne<T>, to be replaced by a single-element tuple (T).
> For what it’s worth, Swift doesn’t have single-element tuples. (T) is just sugar for the type T itself.
Would it be unreasonable to separate those, so that (T) is separate from T instead of being a synonym for it? There is some awkwardness with tuples due to legacy designs. Perhaps this would help clean it up a little (or perhaps make it worse, who knows?)
For source compatibility, we could allow an implicit conversion; in the same way that a T can be implicitly “promoted" to an Optional<T>, it could be implicitly “promoted” to a single-element tuple of T (and vice-versa).
>> We would also be able to remove our limited-arity == overloads in favour of actual, honest-to-goodness Equatable conformance.
> I like this idea though.
>> - Karl
>> swift-evolution mailing list
>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the swift-evolution