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7306 :: Unnecessary var parameter?

• konsumlamm (orginal) [2020-12-30T13:01:03+01:00] view original

  I noticed that some standard library procs have a var parameter when, as far as i can tell, it would suffice to return a new value. For example:

  # from system
  proc new[T](a: var ref T)
  
  # from sets
  proc init[A](s: var HashSet[A]; initialSize = defaultInitialSize)
  
  # from threads
  proc createThread[TArg](t: var Thread[TArg]; tp: proc (arg: TArg); param: TArg)
  Run

  Why don't these look like this instead?

  proc new[T](): ref T
  
  proc init[A](initialSize = defaultInitialSize): HashSet[A]
  
  proc createThread[TArg](tp: proc (arg: TArg); param: TArg): Thread[TArg]
  Run

  Then, using new as an example, one could write this:

  var a = new[int]()
  
  # instead of
  var a: ref int
  new(a)
  Run

  Other procs, like initTable (from tables) already follow this pattern, while newSeq has both options, so there is no real consistency regarding this in the standard library.

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• Araq (orginal) [2020-12-30T16:17:04+01:00] view original

  The primary reason is legacy.

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• jackhftang (orginal) [2020-12-31T07:09:59+01:00] view original

  For new, you can write like this let foo = new(Foo) at least since 1.0.0

  As for hashset and thread, they are not ref/ptr, but value in Nim semantic. And you can call initHashSet() instead of s.init().

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