dictionary fail

dict.swift

/*
  * thread #1: tid = 0x2e1aec, 0x00000001167611ac $__lldb_expr29`Swift._NativeDictionaryStorage.fromArray <A : Swift.Hashable, B>(Swift._NativeDictionaryStorage<A, B>.Type)(Swift.Array<(A, B)>) -> Swift._NativeDictionaryStorage<A, B> + 2284, queue = 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
  * frame #0: 0x00000001167611ac $__lldb_expr29`Swift._NativeDictionaryStorage.fromArray <A : Swift.Hashable, B>(Swift._NativeDictionaryStorage<A, B>.Type)(Swift.Array<(A, B)>) -> Swift._NativeDictionaryStorage<A, B> + 2284
    frame #1: 0x000000011675de35 $__lldb_expr29`Swift.Dictionary.convertFromDictionaryLiteral <A : Swift.Hashable, B>(Swift.Dictionary<A, B>.Type)(Swift.Array<(A, B)>...) -> Swift.Dictionary<A, B> + 69
    frame #2: 0x00000001167569b3 $__lldb_expr29`top_level_code + 2483 at playground29.swift:10
    frame #3: 0x0000000116756cf1 $__lldb_expr29`main + 49 at <EXPR>:0
    frame #4: 0x000000010a7ed510 MyPlayground`get_field_types__XCPAppDelegate + 160
    frame #5: 0x000000010a7ee081 MyPlayground`reabstraction thunk helper from @callee_owned () -> (@unowned ()) to @callee_owned (@in ()) -> (@out ()) + 17
    frame #6: 0x000000010a7eccf1 MyPlayground`partial apply forwarder for reabstraction thunk helper from @callee_owned () -> (@unowned ()) to @callee_owned (@in ()) -> (@out ()) + 81
    frame #7: 0x000000010a7ee0b0 MyPlayground`reabstraction thunk helper from @callee_owned (@in ()) -> (@out ()) to @callee_owned () -> (@unowned ()) + 32
    frame #8: 0x000000010a7ee0e7 MyPlayground`reabstraction thunk helper from @callee_owned () -> (@unowned ()) to @callee_unowned @objc_block () -> (@unowned ()) + 39
    frame #9: 0x000000010ae35abc CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
    frame #10: 0x000000010ae2b805 CoreFoundation`__CFRunLoopDoBlocks + 341
    frame #11: 0x000000010ae2afc3 CoreFoundation`__CFRunLoopRun + 851
    frame #12: 0x000000010ae2aa06 CoreFoundation`CFRunLoopRunSpecific + 470
    frame #13: 0x000000010aed72c1 CoreFoundation`CFRunLoopRun + 97
    frame #14: 0x000000010a7eadcd MyPlayground`top_level_code + 3629
    frame #15: 0x000000010a7ed53a MyPlayground`main + 42
    frame #16: 0x000000010db08145 libdyld.dylib`start + 1
  */
var a = [
  "x":"y",
  "x":"z"
]