What am I missing here? (async)

[xioren]

    import asyncdispatch
    
    
    type testType = object
      testField: bool
    
    
    proc testProc(thing: var testType) {.async.} =
      if not thing.testField:
        thing.testField = true
    
    
    var x: testType
    
    waitFor testProc(x)
    
    
    Run

<https://play.nim-lang.org/#ix=3IGJ>

results in: 
    
    
    Error: 'thing' is of type <var testType> which cannot be captured as it 
would violate memory safety, declared here: /usercode/in.nim(8, 15); using 
'-d:nimNoLentIterators' helps in some cases
    
    
    Run