[swift-evolution] a few initializer proposals

Mike Kluev mike.kluev at gmail.com
Thu Jun 22 18:39:03 CDT 2017

On 23 June 2017 at 00:36, Brian King <brianaking at gmail.com
<brianaking at gmail.com>> wrote:

> A similar syntax has already been proposed and has been `deferred`. There
> are a few other links to discussion in the proposal.
> https://github.com/apple/swift-evolution/blob/master/
> proposals/0018-flexible-memberwise-initialization.md

thank you Brian.

i like the "default value" idea in those proposals. speaking of lazy vars,
maybe just to not have them in the default memberwise initializer param
list at all:

// this is NOT how the language behaves currently:

struct S {
    var a: Int
    var b: Int = 0
    var c: Int?
    var d: Int? = nil // same as c
    var e: Int!
    lazy var f: Int = { return 0 } ()

//  expected "reasonable" default memberwise initializer autogenerated or
//  init(
//      a: Int,
//      b: Int = 0,     // got default value #change
//      c: Int? = nil,  // got implicit default value #change
//      d: Int? = nil,  // got default value #change
//      e: Int!         // no default value - safer
//                      // f is absent due to lazy #change
//  )
//  {
//      self.a = a
//      self.b = b
//      self.c = c
//      self.d = d
//      self.e = e
//                      // f is absent due to lazy #change
//  }

speaking of private var members, if they have an implicit or explicit
default value:

private var g: Int = ...
private var h: Int?
private var i: Int? = ...
private var j: Int!
private var k: Int! = ...

they can be omitted from the parameter list of the default memberwise
initialiser (#change) similar to how lazy vars are omitted above.
if a single private var has no implicit / explicit default value then
default member wise initialiser is not created (#change) and attempt to
opt-in to have one gives an error. let's call it proposal #5. this
particular one is not a backward compatible change, the old code will have
to be modified.

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