Overload the '??' Nil-Coalescing Operator for Custom Swift Types

Written by Team Kodeco

The ?? operator in Swift is used for performing a nil-coalescing operation, which returns the left operand if it’s not nil, otherwise it returns the right operand. When working with custom types in Swift, you may want to overload the ?? operator to perform a similar operation specific to your custom type.

Here’s an example of how you might overload the ?? operator for a custom OptionalString class:

class OptionalString {
  var value: String?
  init(_ value: String?) {
    self.value = value
  }
}

extension OptionalString {
  static func ?? (left: OptionalString, right: OptionalString) -> OptionalString {
    return OptionalString(left.value ?? right.value)
  }
}

Here’s an example of how you might use the overloaded ?? operator on the OptionalString class:

let left = OptionalString("Hello")
let right = OptionalString(nil)
let result = right ?? left
print(result.value!) // Prints "Hello"