I believe there was(was?) already a suggestion to introduce special methods
that could be called from initializers. IMO this is a better solution to
the problem as you really should not call 'usual' instance method until the
instance is fully instantiated(super.init() called in your case):
class MyClass : MySuperClass {
let x : Int
let y : String //let!
initfunc calcY(somePatam: Int) -> String {
return ....
}
init(x: Int) {
self.x = x
self.y = assignY(5)
super.init()
}
}
On 15.06.2016 15:22, Karl via swift-evolution wrote:
Say you have the following code. There is a property on MyClass (‘y’)
which is derived from other data via an instance method; Two-stage
initialisation.
class MySuperClass { init() {} }
class MyClass : MySuperClass {
let x : Int var y : String
init(x: Int) {
self.x = x super.init() y = someInstanceMethod() } }
The code won’t compile because you call super.init before initialising
all properties. The way to work-around this so far is to make the type
of ‘y’ an implicitly-unwrapped optional. I don’t think it’s very elegant
to have to change the type of ‘y’ in this case - it exposes
implementation details and implies that the value may sometimes be nil,
which is not the case.
What about if we allowed you to explicitly declare that it’s okay for
‘y’ not to be initialised before calling super.init? Perhaps by
assigning it to the underscore:
self.x = x y = _ super.init() y = someInstanceMethod()
'y' would still effectively work as an implicitly-unwrapped optional -
the value would be initialised to nil, and any attempt to use it before
it is initialised would be a fatal runtime error as with an IUO. This
also means that it couldn’t be a “let” value.
This change wouldn’t give you any additional safety when using two-stage
initialisation; it would simply not require you to change the type of
the property when doing so.
Thoughts?
Karl _______________________________________________ swift-evolution
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