[swift-evolution] Sparse (fixed-size) array literal syntax
jaden.geller at gmail.com
Fri Jun 2 02:56:23 CDT 2017
Why would this not be possible with fixed sized arrays? Theoretically you could create a type that wrapped a fixed array and make it conform to whatever protocol you want, including the “ExpressibleBy” protocols.
> On Jun 2, 2017, at 12:22 AM, Daryle Walker <darylew at mac.com> wrote:
>> On Jun 2, 2017, at 2:11 AM, Jaden Geller <jaden.geller at gmail.com <mailto:jaden.geller at gmail.com>> wrote:
>> Comments inline.
>>> On Jun 1, 2017, at 10:49 PM, Daryle Walker via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> Current array literal syntax (i.e. “[a, b, c]”) works for dense and/or linear arrays, but isn’t so great later on when we add fixed-size arrays and the defined (non-zero) elements are sparse and/or the array is multi-dimensional (not nested). In these cases I’m thinking of leading each element with its coordinate:
>>> … 6: a, … // complete value, linear array
>> You can already do this with a dictionary since a Int can be used as the key type.
>>> … (1, 2): b, … // complete value, multi-dimensional array
>> This would be possible if tuples of hashable types were considered hahable. Right now, you could define some point type.
>>> … (let x, let y) where y % 2 == 0: c * y + x, … // pattern of qualifying coordinates
>> You can build this sort of thing using an initializer that takes a function. You wouldn’t get this sugar, but I don’t think it is necessary.
>>> … default: d, … // when no other initializer covers an element (Use “_” instead?)
>> This one is a bit harder. I think it would be reasonable for there to exist some subtype of the dictionary literal type that also included information about a default value, but I think this should be motivated by the Swift standard library (e.g. a defaultable dictionary type).
>> Right now, you can just make literal syntax default to a `nil` default value, and then you can define a function that nil-coalesces the default value. This is definitely less elegant, but I don’t think it matters a whole lot.
>> Sparse([1: “foo”, 5: “bar”, 100: “baz”], default: “”)
> I’m not asking how to do this in current Swift with current types, but fixed-sized arrays in a future Swift. I’m asking if this mixing of array- and dictionary-literals for these advanced-array literals would be too hard for compiler implementors to implement.
> Daryle Walker
> Mac, Internet, and Video Game Junkie
> darylew AT mac DOT com
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