generics - Extending Swift's Dictionary to conform to Protocol that requires the use of subscript causes Linker Error -


the title says all, have protocol like: 

protocol myprotocol {     typealias keytype     typealias valuetype      subscript(key: keytype) -> valuetype? { set } }

and trying make dictionary conform myprotocol like:

extension dictionary: myprotocol { }

results in linker error:

undefined symbols architecture x86_64: "__tfvss10dictionarym9subscriptfq_gsqq0__", referenced from:   __ttwuss8hashable___gvss10dictionaryq_q0__18projectname11myprotocols1_fs2_m9subscriptfqqps2_12keytypegsqqs3_15valuetype_ in searcher.o

now, interesting part if reimplement subscript, error goes away, don't know how reimplement without causing infinite recursion.

if instead of { set }, protocol requires { } error goes away , extension works desired.

so imagine issue must in set side of things, trying require { mutating set } doesn't work.

does know (a) what's going on , (b) how make dictionary conform myprotocol, without having resort drastic solutions reimplementing subscript?

at first convinced bug swift, after probing bit, not sure.

i'm using swift 1.2

edit: managed make work doing following:

extension dictionary: myprotocol {     subscript(key: key) -> value? {         {             let index = self.indexforkey(key)              if let = index {                 return self[i].1             }              return nil         }         set {             if let value = newvalue {                 self.updatevalue(value, forkey: key)             } else {                 self.removevalueforkey(key)             }         }     } }

but re-implementing dictionary's subscript doesn't seem idea me.

edit 2: clearer question.

edit 3: tried same code out in swift 2.0 , still doesn't work. curiously linker error different time:

undefined symbols architecture x86_64:   "swift.dictionary.subscript.materializeforset : (a) -> b?", referenced from:       protocol witness _test.myprotocol.subscript.materializeforset : (a.keytype) -> a.valuetype? in conformance <a, b a: swift.hashable> [a : b] : _test.myprotocol in _test in testfile.o


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