Mirror of forum.nim-lang.org

2408 :: Generic not nil

• beltsonata (orginal) [2016-07-25T20:52:49+02:00] view original

  I'm new to nim and I don't understand why this doesn't work.

  type
    Thing = ref object
      value: int
  
  proc function(thing: Thing not nil): void =
    discard
  
  proc not_nil*[T](obj: T): T not nil =
    if obj.isNil:
      assert false
    else:
      result = obj
  
  let t = Thing()
  
  function(not_nil(t))
  Run

  not_nil.nim(16, 17) Error: cannot prove 'not_nil(t)' is not nil

  Is this a bug? Many thanks.

---

• _tulayang (orginal) [2016-07-26T02:49:14+02:00] view original

  try:

  type
    ThingObj = object
      value: int
    
    Thing = ref ThingObj not nil
  
  proc function(thing: Thing): void =
    discard
  
  proc not_nil*[T](obj: T): T =
    if obj.isNil:
      assert false
    else:
      result = obj
  
  let t = Thing()
  
  function(not_nil(t))
  Run

---

• beltsonata (orginal) [2016-07-26T19:42:02+02:00] view original

  Thanks, that works.

---