ios - Swift: function overload resolution via closure parameter? -

i trying solve separate problem related parsing json. in process, ran afoul of swift compiler, expected use closure template arguments select function overload optional types.

i haven't seen explicit in documentation on topic, not expectation else equal, swiftc use arguments of closure parameter in generic function select correct overload?

here simplest sample come with:

import foundation  let os:nsstring = "foo!" let d:[string:anyobject] = ["a": os]  struct model {     var opt:string?     var basic:string = "" }   func read<t>(source:anyobject?, set:t -> ()) {     if let t:t = source as? t {         println("basic: read type: \(t.self) value \(source)")     }     else {         println("failed read basic type \(t.self) value \(source)")     } }   func read<t>(source:anyobject?, set:t? -> ()) {      assert(false, "this not called")      if let t:t? = source as? t? {         println("optional: read optional type: \(t.self) value \(source)")     }     else {         println("failed read optional type \(t.self) value \(source)")     } }   var m = model() println(m) let raw: anyobject? = d["a"]  struct property<t> {     typealias v = t     var get:() -> t     var set:t -> ()      func doread(d:[string:anyobject]) {         read(d["a"], set)     } }  let b = property(get: { m.basic }, set: { v in m.basic = v }) b.doread(d)  let o = property(get: { m.opt }, set: { v in m.opt = v }) o.doread(d) 

per comment inline, expected second overload used optional types, not. missing something?

edit

note compiler inferring optional / non optional type property construct - knows closure takes optional, doesn't select overload. have restored of original logging code above, , output is:

basic: read type: swift.string value optional(foo!)

failed read basic type swift.optional value optional(foo!)

from usage of swift, see compiler prefers non-optionals on optionals. operation:

let o = property(set: { v in m.opt = v })

is legal when v non-optional, , therefore compiler assumes such.

this question, , assume lot of other questions answered when swift made open-source.