If case logical operator integration

Evolution Discussion
1

Hello!

Have you ever considered the convenience of integrating the if case syntax with && or || operators?
This enhancement could prove particularly handy for enums with multiple cases, especially in scenarios where employing a switch statement feels excessive.

For instance:

enum MyEnum {
	case first(data: String)
	case second(data: String)
	case third(data: [String])
	case fourth
	case fifth
	case sixth
}
let first = MyEnum.first(data: "Gabriel")
let second = MyEnum.second(data: "Aurora")
var third = MyEnum.third(data: ["Gabriel", "Aurora", "Marcela"])

if case .first(let data) = first || case .second(let data) = second {
    print(data)
}

In this envisioned implementation, I imagine that utilizing || would require all cases to possess parameters of the same type (as demonstrated above) or no parameters at all. Conversely, with &&, compatibility would extend to any combination of parameters.

Consider:

if case .first(let firstData) = first && case .second(let secondData) = second && case .third(let thirdData) = third {
    print(firstData)
    print(secondData)
    print(thirdData)
}

What do you think?

2

This can already be done, it's just spelled with , rather than &&.

3

The || though is not easy. For the type (I changed your type a bit to add more use cases):

enum MyEnum {
    case first(string: String)
    case second(string: String)
    case third(strings: [String], someInt: Int)
    case fourth(Int, Double)
    case fifth
}

My long standing wish is to have an autogenerated code:

extension MyEnum: SomeMagicProtocol {
    // Autogenerated conformances
    var first: String! {
        get {
            if case .first(let string) = self { string } else { nil }
        }
        set {
            self = .first(string: newValue)
        }
    }
    var second: String! {
        get {
            if case .second(let string) = self { string } else { nil }
        }
        set {
            self = .second(string: newValue)
        }
    }
    var third: (strings: [String], someInt: Int)! {
        get {
            if case let .third(strings, someInt) = self { (strings: strings, someInt: someInt) } else { nil }
        }
        set {
            self = .third(strings: newValue.strings, someInt: newValue.someInt)
        }
    }
    var fourth: (Int, Double)! {
        get {
            if case let .fourth(x, y) = self { (x, y) } else { nil }
        }
        set {
            self = .fourth(newValue.0, newValue.1)
        }
    }
    var fifth: MyEnum! {
        get {
            if case .fifth = self { .fifth } else { nil }
        }
        set {
            self = .fifth
        }
    }
}

which could happen when my type marked with SomeMagicProtocol.

protocol SomeMagicProtocol {}

Here's how your example could look like then:

let a = MyEnum.first(string: "Gabriel")
let b = MyEnum.second(string: "Aurora")

if let string = a.first ?? b.second {
    print(string)
}
if let strings = a.third?.strings {
    print(strings)
}
4

It's not difficult. As the case spelling would hint, you switch over the two values:

switch (first, second) {
case (.first(let data), _):
  fallthrough
case (_, .second(let data)):
  print(data)
default:
  break
}
1 Like
5

Much of this can be accomplished using macros, such as PointFree’s swift-case-paths, to generate the Bool accessors for each case. I still think it would be better for this to be built it, and for the case syntax to be better integrated, but there are workarounds now.

6

Yeah, for what it's worth, using our case paths library your first situation can be expressed like so:

import CasePaths

@CasePathable
@dynamicMemberLookup
enum MyEnum {
	case first(data: String)
	case second(data: String)
	case third(data: [String])
	case fourth
	case fifth
	case sixth
}
let value1 = MyEnum.first(data: "Gabriel")
let value2 = MyEnum.second(data: "Aurora")
var value3 = MyEnum.third(data: ["Gabriel", "Aurora", "Marcela"])

if let data = value1.first ?? value2.second {
    print(data)
}

And your second situation like this:

if
  let data1 = value1.first,
  let data2 = value2.second,
  let data3 = value3.third
{
  print(data1)
  print(data2)
  print(data3)
}

And there are a few other niceties too, such as an expression version of case pattern matching:

if value1.is(\.first) {
  // ...
}

Of course, this is only viable if you are OK depending on a 3rd party library and OK with the cost of macros.

6 Likes