[swift-users] Static type when expecting dynamic type

[Howard Lovatt]

Thanks for your prompt responses.

Have filed a bug:

SR-3840 - Closure picks up static type not dynamic
<https://bugs.swift.org/browse/SR-3840>

  -- Howard.

On 3 February 2017 at 08:57, Slava Pestov <spestov at apple.com> wrote:

> The problem is were not marking the materializeForSet accessor
> in DefaultMutableReference.value as an override. Definitely a bug:
>
> sil_vtable DefaultMutableReference {
>   #MutableReference.init!initializer.1: _TFC1d23DefaultMutableReferencecfT_GS0_x_
>     // DefaultMutableReference.init() -> DefaultMutableReference<A>
>   #MutableReference.value!getter.1: _TFC1d23DefaultMutableReferenceg5valuex
>   // DefaultMutableReference.value.getter
>   #MutableReference.value!setter.1: _TFC1d23DefaultMutableReferences5valuex
>   // DefaultMutableReference.value.setter
>   #MutableReference.value!materializeForSet.1: _
> TFC1d16MutableReferencem5valuex // MutableReference.value.
> materializeForSet
>   #DefaultMutableReference.value!materializeForSet.1: _
> TFC1d23DefaultMutableReferencem5valuex   // DefaultMutableReference.value.
> materializeForSet
>
> The last entry should not exist.
>
> I’ll have a fix shortly.
>
> Slava
>
> On Feb 2, 2017, at 9:04 AM, Jordan Rose via swift-users <
> swift-users at swift.org> wrote:
>
> Seems like a bug, and moreover it seems like a regression from Swift 3.0.
> Mind filing a report at bugs.swift.org?
>
> Thanks!
> Jordan
>
> On Feb 1, 2017, at 20:49, Howard Lovatt via swift-users <
> swift-users at 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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