How to avoid memory capture violation during addExitProc capture?

[Yardanico]

This isn't what @boia01 meant at all, you need to make a safe reference, not 
cast the raw pointer to a traced Nim reference, that's invalid code and it'll 
likely crash.

An example of working code would be this:
    
    
    # Example of proc memory capture violation
    
    import
      flatty, # https://github.com/treeform/flatty - for actual persistence
      std/[exitprocs, os, times]
    
    type
      HistoryEntry  = string
      History = ref object
        entries: seq[HistoryEntry]
    
    proc save(history: History, filename: string) =
      writeFile(filename, history.toFlatty)
    
    proc persistence(history: var History, filename: string) =
      if fileExists filename:
        history = filename.readFile.fromFlatty History
      
      let history = history # make a non-var history so we can capture it
      
      addExitProc(
        proc() =
          save(history, filename)
          # Error: 'history' is of type <var History> which cannot be captured 
as
          # it would violate memory safety, declared here:
          # /Users/DM/work/trunk/nim/test_persistence.nim(10, 11); using
          # '-d:nimNoLentIterators' helps in some cases
      )
    
    # Example usage
    const historyFilename = "history.his"
    var history = History()
    
    history.persistence historyFilename
    echo history.entries # so far
    history.entries.add "Another entry: " & $now() # Add another entry on each 
run
    
    
    Run

There are probably other ways, but this is what I came up with.