swift - Ambiguous type inference -


i'm getting compiler error swift 3.0.1 that's got me stumped. error states there's ambiguity in type of computed property can't see how.

i have protocol generic property root. protocol has generic constraint root must subclass of type root.

class root { }  protocol generic {     associatedtype roottype: root     var root: roottype { } }

i define protocol extension states:

if generic subclass of root, return self root property.

so basically: if it's root, can forward self.

extension generic self: root {     var root: self {         return self     } }

i have genericwrapper class subclass of root , wraps instance of generic (to perform root operations generic proxy).

class genericwrapper<t: generic>: root {     var generic: t      init(generic: t) {         self.generic = generic     } }

finally, define specialised protocol, , extension states:

if specialised implements generic, return genericwrapper root property.

protocol specialised { } extension specialised self: generic {     var root: genericwrapper<self> {         {             return genericwrapper(generic: self)         }     } }

then when try implement class implements generic , specialised, i'm getting error.

class specialisedimplementation: generic, specialised {     // errors:     //   ambiguous inference of associated type 'roottype': 'genericwrapper<specialisedimplementation>' vs. 'specialisedimplementation'     //   matching requirement 'root' declaration inferred associated type 'genericwrapper<specialisedimplementation>'     //   matching requirement 'root' declaration inferred associated type 'specialisedimplementation' }

the reason i'm confused because ambiguity states specialisedimplementation class matches requirement extension generic when generic: root, specialisedimplementation doesn't inherit root shouldn't surely?

the diagnostic confusing; real problem here it's circular , it's going beyond compiler can handle.

it tries resolve generic, , finds can't without assuming specialisedimplementation subclass of root (which isn't true, it's desperate find way make work). , tries make specialised work, can if generic worked, way generic work make root.

you want assume true @ same time, it's not smart. it's trying build piecemeal, 1 protocol @ time, , gets confused. open bugreport @ bugs.swift.org.

(but wildly complicated. in particular, i'd work hard rid of root class if possibly can; mixing protocols , classes , generics recipe lots of confusing compiler problems.)


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