SE-0258: Property Wrappers (second review)

Evolution Proposal Reviews
151

Implicitly, when no initializer is provided and the property wrapper type provides a no-parameter initializer ( init() ). In such cases, the wrapper type's init() will be invoked to initialize the stored property.

You can create Default like so

protocol Initializable {
  init()
}

extension String: Initializable {}

@propertyWrapper
struct Default<Value> where Value: Initializable {
  var wrappedValue: Value
  init() {
    wrappedValue = Value.init()
  }
}

@Default var foo: String

// translates to (I'm going to use the `_` form which has been discussed recently)
private var _foo = Default<String>()

var foo: String {
  ...
}
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