Optional Chaining / map / flatMap (Optional)

// Optional Chaining
optional?.property
optional?.method()

// Chained access (if any link is nil, the whole expression is nil)
optional?.propertyA?.propertyB

// Optional map / flatMap
optional.map { $0 + 1 }        // nil if nil; otherwise transforms the value
optional.flatMap { Int($0) }   // nil if nil or if the conversion fails

// Basic Optional Chaining
class Address {
    var city: String
    init(city: String) { self.city = city }
}

class Person {
    var name: String
    var address: Address?
    init(name: String, address: Address? = nil) {
        self.name = name
        self.address = address
    }
}

let taro = Person(name: "Taro", address: Address(city: "Tokyo"))
let hanako = Person(name: "Hanako")  // no address

// Safe access via Optional Chaining (nil-safe)
print(taro.address?.city ?? "Unknown")    // Tokyo
print(hanako.address?.city ?? "Unknown")  // Unknown

// Optional map
let optNumber: Int? = 5
let doubled = optNumber.map { $0 * 2 }  // Optional(10)
let nilNumber: Int? = nil
let nilDoubled = nilNumber.map { $0 * 2 }  // nil

print(doubled ?? 0)    // 10
print(nilDoubled ?? 0) // 0

// flatMap (avoids nested Optionals)
let strNumber: String? = "42"
let parsed = strNumber.flatMap { Int($0) }  // Optional(42)
let invalid: String? = "abc"
let failedParsed = invalid.flatMap { Int($0) }  // nil

print(parsed ?? -1)       // 42
print(failedParsed ?? -1) // -1

// compactMap on an array
let strings = ["1", "two", "3", "four", "5"]
let integers = strings.compactMap { Int($0) }
print(integers)  // [1, 3, 5]

Optional Chaining (?.) lets you safely navigate complex object structures with multiple nested Optionals. If any link in the chain is nil, evaluation stops at that point and the entire expression returns nil.

map transforms the value inside an Optional and returns the result as an Optional. Use flatMap when the transform function itself returns an Optional — it flattens the result to avoid a nested Optional<Optional<T>>. Because Optional Chaining always produces an Optional, you must unwrap the result before using it.

For the basics of Optionals, see Optional / ? / !.