Improvements to synthesized memberwise initializers

Paul Hudson      @twostraws

SE-0242 introduced major improvements to one of Swift’s most commonly used features: memberwise initializers for structs.

In earlier versions of Swift, a memberwise initializer was automatically created to accept parameters matching the properties of a struct, like this:

struct User {
    var name: String
    var loginCount: Int = 0
}

let piper = User(name: "Piper Chapman", loginCount: 0)

In Swift 5.1 this has been enhanced so that the memberwise initializer now uses default parameter values for any properties that have them. In the User struct we’ve given loginCount a default value of 0, which means we can either specify it or leave it to the memberwise initializer:

let gloria = User(name: "Gloria Mendoza", loginCount: 0)
let suzanne = User(name: "Suzanne Warren")

This lets us avoid repeating code, which is always welcome.

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Other changes in Swift 5.1…

• Implicit returns from single-expression functions
• Universal Self
• Opaque return types
• Static and class subscripts
• Warnings for ambiguous none cases
• Matching optional enums against non-optionals
• Ordered collection diffing
• Creating uninitialized arrays

Download all Swift 5.1 changes as a playground Link to Swift 5.1 changes

Browse changes in all Swift versions