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The optional pattern is syntactic sugar used within Swift’s pattern matching engine to match and extract the wrapped value of an Optional<Wrapped> enumeration. It allows developers to match against the .some(Wrapped) case using the ? suffix instead of explicitly writing out the underlying enumeration case. Under the hood, Swift defines optionals as a generic enumeration: 
enum Optional<Wrapped> {
    case none
    case some(Wrapped)
}
When the compiler encounters an optional pattern, it translates the ? syntax directly into a .some(Wrapped) enumeration pattern. This pattern can be applied in any context that supports Swift pattern matching, including switch statements, if case, guard case, and for case loops.

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Syntax Equivalence

The optional pattern is functionally identical to the explicit enumeration pattern. Value Binding in a Switch Statement: 
let target: Int? = 42

// Explicit Enumeration Pattern
switch target {
case .some(let unwrappedValue):
    print(unwrappedValue)
case .none:
    break
}

// Equivalent Optional Pattern
switch target {
case let unwrappedValue?:
    print(unwrappedValue)
case nil:
    break
}
Value Binding in Conditionals: 
// Explicit Enumeration Pattern
if case .some(let unwrappedValue) = target {
    // ...
}

// Equivalent Optional Pattern
if case let unwrappedValue? = target {
    // ...
}
Filtering in Iteration: 
let sequence: [Int?] = [1, nil, 3, nil, 5]

// Explicit Enumeration Pattern
for case .some(let unwrappedValue) in sequence {
    // ...
}

// Equivalent Optional Pattern
for case let unwrappedValue? in sequence {
    // ...
}

​
Literal Matching

The optional pattern is not restricted to variable binding (let or var). It can also be used to match specific literal values wrapped inside an optional. The ? suffix is appended directly to the literal. 
let status: Int? = 200

// Matches only if the optional contains exactly .some(200)
if case 200? = status {
    // ...
}

// Equivalent to:
if case .some(200) = status {
    // ...
}

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Technical Characteristics

  1. Syntactic Token: The ? in an optional pattern is a built-in syntactic token defined by the Swift grammar, not an operator. Because it is not an operator, it is not subject to operator overloading. It strictly serves as a pattern matching token and should not be confused with optional chaining (obj?.property) or the ternary operator (a ? b : c).
  2. Binding Placement: When binding a variable, the ? must be placed immediately after the variable name being bound, not after the let or var keyword (e.g., let x?, never let? x).
  3. Type Inference: The compiler infers the type of the bound variable as the Wrapped type of the optional. If the matched value is String?, the bound variable using the optional pattern is strictly String.
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