Expression pattern operator ~=

pattern.matching.swift

import UIKit

class A {
    var value: Int
    
    init(value: Int) {
        self.value = value
    }
}

extension A: Comparable {}

func == (lhs: A, rhs: A) -> Bool {
    return lhs.value == rhs.value
}

func < (lhs: A, rhs: A) -> Bool {
    return lhs.value <= rhs.value
}

// MARK: Pattern matching

func ~=(pattern: [A], value: A) -> Bool {
    return pattern.contains(value)
}

func ~=(pattern: A, value: [A]) -> Bool {
    return value ~= pattern
}

// Example

let array1 = [A(value: 1), A(value: 5)]
let array2 = [A(value: 3), A(value: 4)]

let a = A(value: 1)

switch a {
case array1: print("Matched on array1")
case array2: print("Matched on array2")
default: print("Not matched")
}

switch array1 {
case a: print("`a` matched")
default: print("Not matched")
}

// Output:
// "Matched on array1"
// "`a` matched"