swift - Fail to imply _Reflectable protocol -

i reading mirrortype @ nshipster,and trying adopt it's code swift 2.1. works fine until when tried custom _mirrortypewith :

extension wwdcsession : _reflectable {     func _getmirror() -> _mirrortype {        return wwdcsessionmirror(self)     } } 

an error occured :

error: playground execution aborted: execution interrupted, reason: exc_bad_access (code=2, address=0x7fff58273e87).

and found out it's because init method in wwdcsessionmirror being called infinite times.

struct wwdcsessionmirror: _mirrortype { private let _value: wwdcsession  init(_ value: wwdcsession) {     _value = value }  var value: { return _value }  var valuetype: any.type { return wwdcsession.self }  var objectidentifier: objectidentifier? { return nil }  var disposition: _mirrordisposition { return .struct }  var count: int { return 4 }  subscript(index: int) -> (string, _mirrortype) {     switch index {     case 0:         return ("number", _reflect(_value.number))     case 1:         return ("title", _reflect(_value.title))     case 2:         return ("track", _reflect(_value.track))     case 3:         return ("summary", _reflect(_value.summary))     default:         fatalerror("index out of range")     } }  var summary: string {     return "wwdcsession \(_value.number) [\(_value.track.rawvalue)]: \(_value.title)" }  var quicklookobject: playgroundquicklook? {     print(summary)     return .text(summary) } } 

i want ask why happened , , how fix it?

_reflectable , _mirrortype not droids you're looking for.

they legacy types, have been superseded customreflectable (among others). 2015 wwdc session lldb goes detail (disclaimer: speaker of part of session, conflict of interests around :-)

but, anyway, issue you're running because of line:

_value = value 

since you're typing line in playground, tells playground logic capture display ("log" in playground parlance) thing you're assigning. so, playground uses mirror attached type. so, go off , create one, causes run

_value = value 

again, tells playground logic log value, means create mirror, ...

you should first of check if can adopt mirror , customreflectable instead of _mirrortype , if using apis fixes problem. if doesn't possible workaround put reflection support code in auxiliary source file cause playground logic not log things inside of it.