Swift pattern examples for the swift, for, and guard keywords

pattern-examples.swift

import Foundation

// 1. Wildcard Pattern
func wildcard(a: String?) -> Bool {
    guard case _? = a else { return false }
    
    for case _? in [a] {
        return true
    }
    
    switch a {
    case _?: return true
    case nil: return false
    }
}
wildcard("yes")
wildcard(nil)

// 2. Identifier Pattern
func identifier(a: Int) -> Bool {
    guard case 5 = a else { return false }
    for case 5 in [a] {
        return true
    }
    switch a {
    case 5: return true
    default: return false
    }
}
identifier(5)

// 3. Value Binding Pattern
// 4. Tuple Pattern
// 5. Type Casting Pattern
func valueTupleType(a: (Int, Any)) -> Bool {
    guard case let (x, _ as String) = a else { return false}
    print(x)
    
    for case let (a, _ as String) in [a] {
        print(a)
        return true
    }
    
    switch a {
    case let (a, _ as String):
        print(a)
        return true
    default: return false
    }
}
let u: Any = "a"
let b: Any = 5
print(valueTupleType((5, u)))
print(valueTupleType((5, b)))


// 6. Enumeration Pattern
enum Test {
    case T1(Int, Int)
    case T2(Int, Int)
}

func enumeration(a: Test) -> Bool {
    guard case .T1(_, _) = a else { return false }
    
    for case .T1(_, _) in [Test.T1(1, 2)] {
        return true
    }
    
    switch a {
    case .T1(_, _): return true
    default: return false
    }
}
enumeration(.T1(1, 2))
enumeration(.T2(1, 2))

// 7. Expression Pattern
struct Soldier {
    let hp: Int
}

func ~= (pattern: Soldier, value: Soldier) -> Bool {
    return pattern.hp == value.hp
}

func expression(a: Soldier) -> Bool {
    guard case Soldier(hp: 10) = a else { return false }
    
    for case Soldier(hp: 10) in [a] {
        return true
    }
    
    switch a {
    case Soldier(hp: 10): return true
    default: return false
    }
}

expression(Soldier(hp: 10))
expression(Soldier(hp: 11))