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2792 :: any type and proc pointer!

• Mirai (orginal) [2017-02-11T13:43:27+01:00] view original

  so, i have a problem i've got from this code:

  type item[T] = object
      value: any
      next: ptr any
  Run

  >next is ptr any cause i dont wanna write smth like >next: ptr item[any]. i'm afraid of gettin error about auto in contexts. can i get an object with pointer on other with non-same type? like that

  var i: item[int] #actually there is error: Error: invalid type: 'auto' in this context: 'item[system.int]'. AND YES I KNOW: VALUE: T and NEXT: ptr item[T]/T will work
  var tmp: item[string]
  i.value = 3
  i.next = addr(tmp)
  ...
  Run

  or its impossible in that way?

  and the second problem is: how can i transfer a pointer on proc to other proc? example:

  proc a(p: ptr proc) {.procvar.} =
   ...
  
  a(addr(`<`))
  Run

  i've got error >Expression has no address. (on other comp i've got msg that proc is not procvar, lol) help me resolve THOSE PROBLEMS PLEASE AAAAAA

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• Mirai (orginal) [2017-02-11T13:53:49+01:00] view original

  actually, on

  type item = object
      value: any
      next: ptr item
  Run

  i get >'any' is not a concrete type. (i think its cause all types like >any are generics)

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• jcosborn (orginal) [2017-02-11T16:34:57+01:00] view original

  Yes, 'any' is a generic (typeclass). Your object should probably be defined like this

  type item[T] = object
    value: T
    next: ptr item[T]
  Run

  Likewise '<' is an overloaded proc, so not a specific proc that you can pass to a function. Also, you don't need to specify 'ptr' for a proc when used as an argument, Nim will implicitly do the right thing for the corresponding backend. You can wrap overloaded functions in a specific one if you want to pass them

  proc a(p: proc) =
    var x,y: int
    echo p(x,y)
  
  proc lt(x,y: int): bool =
    x < y
  
  a(lt)
  Run

  or you can use a template to generate separate functions for each proc you want passed in. This can then handle overload procs.

  template makeproc(f,p: untyped): untyped =
    proc f =
      var x,y: int
      echo p(x,y)
  
  makeproc(b, `<`)
  b()
  Run

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