if let / guard let (Optional Binding)

// if let
if let constantName = optionalValue {
    // constantName is available here (non-Optional)
}

// if var (mutable)
if var variableName = optionalValue {
    variableName = newValue  // can be modified
}

// Unwrap multiple Optionals at once
if let a = optA, let b = optB, a > 0 {
    // runs only if both a and b are non-nil, and a is greater than 0
}

// Swift 5.7+: shorthand with the same name
if let name {
    // unwraps name (Optional) and uses it under the same name
}

// Basic if let
let input: String? = "42"
if let value = Int(input!) {
    print("Conversion succeeded: \(value)")
} else {
    print("Conversion failed")
}

// Unwrap multiple Optionals at once
let firstName: String? = "Taro"
let lastName: String? = "Yamada"

if let first = firstName, let last = lastName {
    print("Full name: \(last) \(first)")
}

// Check a condition at the same time
let score: Int? = 85
if let s = score, s >= 60 {
    print("Passed: \(s) points")
}

// Shorthand syntax (Swift 5.7+)
let name: String? = "Hanako"
if let name {
    print("Hello, \(name)!")  // use name directly
}

// Using guard let
func printLength(of str: String?) {
    guard let str = str else {
        print("No string provided")
        return
    }
    print("Character count: \(str.count)")
}

printLength(of: "Hello")
printLength(of: nil)

Optional Binding (if let / guard let) is the most fundamental and safe way to work with Optionals in Swift. Once unwrapped, the constant or variable is treated as non-Optional within its scope.

When unwrapping multiple Optionals at once, if even one of them is nil, the else branch (or the guard else branch) is executed. An unwrapped constant is valid only within the corresponding if/guard block (with guard let, it is valid for the entire enclosing scope).

For the operator that returns a default value when nil, see ?? (Nil-Coalescing Operator).