Seems like a bug, and moreover it seems like a regression from Swift 3.0. Mind
filing a report at bugs.swift.org <http://bugs.swift.org/>?
Thanks!
Jordan
> On Feb 1, 2017, at 20:49, Howard Lovatt via swift-users
> <swift-users@swift.org> wrote:
>
> Hi All,
>
> Anyone know what is going on here:
>
> //: Closure picks up static type not dynamic
>
> class MutableReference<T> {
> init() {
> guard type(of: self) != MutableReference.self else {
> fatalError("MutableReference is an abstract class; create a
> derrivative of MutableReference")
> }
> }
> var value: T {
> get {
> fatalError("Calculated property value getter should be
> overridden")
> }
> set {
> fatalError("Calculated property value setter should be
> overridden")
> }
> }
> }
>
> class DefaultMutableReference<T>: MutableReference<T> {
> private var _value: T
> override var value: T {
> get {
> return _value
> }
> set {
> _value = newValue
> }
> }
> init(_ value: T) {
> _value = value
> }
> }
>
> let e: (MutableReference<[Int]>, Int) -> Void = { $0.value.append($1) }
> let dmr = DefaultMutableReference([2])
> dmr.value // [2]
> e(dmr, 2) // fatal error: Calculated property value getter should be
> overridden
> dmr.value // Expect [2, 2]
> If I change `e` to:
>
> let e: (DefaultMutableReference<[Int]>, Int) -> Void = {
> $0.value.append($1) }
> It works fine.
>
> IE the closure is using the static type of its first argument and not
> dynamically dispatching.
>
> Am I doing something wrong? Is there a way round where I can still use the
> base class for `e`?
>
>
>
> Thanks for any help in advance,
>
> -- Howard.
>
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