[swift-users] Generic initializer's parameter type not being resolved

[Hooman Mehr]

Update your where clause to:

        where Type: PluginDataProtocol, Type.Parent == Monster {


> On Jan 31, 2017, at 10:36 AM, Andrey Fidrya via swift-users <swift-users at swift.org> wrote:
> 
> Hi All,
> 
> I've encountered a very strange problem where generic initializer's parameter type isn't resolved correctly unless explicitly casted.
> 
> Below is playground code for reproducing the problem and compiler error I'm getting.
> After removing "as! Type.Parent" cast the code won't compile anymore...
> 
> It expects Type.Parent and I'm passing Monster, but Parent is typealiased to Monster.
> Why can't it infer the type automatically?
> 
> 
> public protocol PluginDataProtocol: class {
>     associatedtype Parent
>     init(parent: Parent)
> }
> 
> public class Monster {
>     public var pluginsData = [ObjectIdentifier: AnyObject]()
>     
>     public func pluginData<Type>(id: ObjectIdentifier = ObjectIdentifier(Type.self)) -> Type
>                 where Type: PluginDataProtocol {
>         if let data = pluginsData[id] as? Type {
>             return data
>         } else {
>             let data = Type(parent: self as! Type.Parent)
>             pluginsData[id] = data
>             return data
>         }
>     }
> }
> 
> final class MyMonsterPluginData: PluginDataProtocol {
>     typealias Parent = Monster
>     
>     weak var parent: Parent?
>     
>     init(parent: Parent) {
>         self.parent = parent
>     }
> }
> 
> Compiler error:
> 
> Playground execution failed: error: Generics.playground:14:24: error: cannot invoke initializer for type 'Type' with an argument list of type '(parent: Monster)'
>             let data = Type(parent: self /* as! Type.Parent */)
>                        ^
> 
> Generics.playground:14:24: note: expected an argument list of type '(parent: Self.Parent)'
>             let data = Type(parent: self /* as! Type.Parent */)
> 
> 
> Regards,
> Andrey
> 
> 
> 
> _______________________________________________
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> swift-users at swift.org
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