Add custom pattern matching to make your switch statements magical

CustomMatcher.swift

struct CustomMatcher<Value> {
    let closure: (Value) -> Bool
    static func ~= (caseValue: CustomMatcher<Value>, switchValue: Value) -> Bool {
        caseValue.closure(switchValue)
    }
    static func ~= (caseValue: Value, switchValue: CustomMatcher<Value>) -> Bool {
        switchValue.closure(caseValue)
    }
}

extension CustomMatcher where Value == String {
    static func hasPrefix(_ prefix: String) -> CustomMatcher {
        CustomMatcher { $0.hasPrefix(prefix) }
    }
}

extension CustomMatcher where Value: Collection {
    static var isEmpty: CustomMatcher {
        CustomMatcher { $0.isEmpty }
    }
}

// random just so that playground doesn't find it deterministic at compile time
let string = "Hello-\(Int.random(in: 0..<10))"

// Apply different custom operators/matchers on different cases:
switch string {
  case .isEmpty: print("Nothing to say?")
  case "a": print("Is 'a'")
  case "b": print("Is 'b'")
  case .hasPrefix("Hello"): print("Hello to you too!")
  default: print("Huh?")
}
// "Hello to you too!"


// If you happen to want to apply the same operator on all the cases, you can apply it on the switch instead:
switch CustomMatcher.hasPrefix(string) {
  case "a": print("Starts with 'a'")
  case "b": print("Starts with 'b'")
  case "Hello": print("Hello to you too!")
  default: print("Huh?")
}
// "Hello to you too!"