Fixing Angle Bracket Blindness (and unboxing existentials while we're at it...)

[Douglas_Gregor]

@jeremyabannister

Here's the idea:

A couple of these overlap significantly with other ideas that have been recently discussed, so I'll point those out here.

@jeremyabannister

func doSomething (with value: <Value>)

As Kyle noted, this use case is subsumed by opaque parameters, a Swift 5.7 feature that was recently accepted and implemented as SE-0341. This example would be written as:

func doSomething(with value: some Any)

@jeremyabannister

Allows Constraints

func first (of collection: <C: Collection>) -> C.Element

SE-0326, which is under active review right now, composes with SE-0341 to allow one to specify, e.g., the element type of generic collections. Your example doesn't translate precisely, but it's very much in the same space. I do think it makes the case for your suggested syntax a much harder sell, because it's eliminating the angle brackets entirely in a subset of the use cases.

@jeremyabannister

Allows Generic Computed Properties

var anyKindOfSevenYouWant: <T: ExpressibleByIntegerLiteral> {
    .init(integerLiteral: 7)
}

I think generic computed properties would be a good feature on its own, and is orthogonal to the syntax you describe.

@jeremyabannister

let boxedUpValue: some Equatable = ...
let value: <Value> = boxedUpValue
if let dynamicallyCasted = someOtherValue as? Value {
    print(value == dynamicallyCasted)
}

There's an active pitch on implicitly opening existentials that's in the same spirit as this.

@jeremyabannister

Extensions On Any

extension <T> {
    func mutated (by mutation: (inout Self)->()) -> Self {
        var copy = self
        mutation(&copy)
        return copy
    }
}

Another separable and good feature, which we often call "parameterized extensions".

Doug