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 <dary...@mac.com> wrote: > >> >> On Jun 2, 2017, at 2:11 AM, Jaden Geller <jaden.gel...@gmail.com >> <mailto:jaden.gel...@gmail.com>> wrote: >> >> Comments inline. >> >>> On Jun 1, 2017, at 10:49 PM, Daryle Walker via swift-evolution >>> <swift-evolution@swift.org <mailto:swift-evolution@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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