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4252 :: collections of procs[T]()

• mitai (orginal) [2018-09-29T03:22:35+02:00] view original

  is there a way to have a collection (seq or better: Tables) of procs with generic types?

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• mratsim (orginal) [2018-09-29T09:21:04+02:00] view original

  Yes you can, see this for example: https://github.com/mratsim/nim-rmad/blob/master/src/autograd.nim#L46-L57

  Note that the proc arity (number of arguments) is part of the type, as is its calling convention (pointer/{.nimcall.} vs {.closure.}).

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• mitai (orginal) [2018-09-29T16:46:04+02:00] view original

  Thankyou for your reply @mratsim

  I tried the following:

  type
      Data*[T] = object
        id: string
        contents: T
        subscribers: seq[proc(d: T)]
    
    
    proc addSubscriber*[T](d: T, cb: proc(d:T)) =
      d.subscribers.add(cb)
    
    proc callSubscribers[T](d: T) =
      for cb in d.subscribers:
        cb(d.contents)
    
    var dd = Data[string]()
    dd.contents = "a content"
    dd.id = "1"
    dd.subscribers = newseq[proc(d: string)]()
    dd.addSubscriber(proc(d: string) = echo $d)
    
    dd.callSubscribers()
  
  Run

  but I get this error:

  
    testproc.nim(19, 3) Error: type mismatch: got <Data[system.string], proc (d: string {.gcsafe, locks: 0.}>
    but expected one of:
    proc addSubscriber[T](d: T; cb: proc (d: T))
      first type mismatch at position: 2
      required type: proc (d: T){.closure.}
      but expression 'proc (d: string) = echo [$d]' is of type: proc (d: string){.gcsafe, locks: 0.}
    
    expression: addSubscriber(dd, proc (d: string) = echo [$d])
  Run

  it seems I'm missing something

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• LeuGim (orginal) [2018-09-29T21:08:54+02:00] view original

  proc addSubscriber*[T](d: var Data[T], cb: proc(d:T)) =
    d.subscribers.add(cb)
  Run

  A typo T for Data[T], and var needed for add.

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• mitai (orginal) [2018-09-29T22:43:11+02:00] view original

  Thank you!

  this does work:

  type
    Data*[T] = object
      contents: T
      subscribers: seq[proc(d: T)]
  
  proc createData*[T](t: typedesc[T], c: T): Data[T] =
    result = Data[T]()
    result.contents = c
    result.subscribers = @[]
  
  proc addSubscriber*[T](d: var Data[T], cb: proc(d:T)) =
    d.subscribers.add(cb)
  
  proc callSubscribers[T](d: T) =
    for n in d.subscribers:
      n(d.contents)
  
  var dd = createData(string, "data")
  proc print[T](d: T) =
    echo $d
  
  dd.addSubscriber(print)
  
  dd.callSubscribers()
  Run

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