Mirror of forum.nim-lang.org

1063 :: [Solved] What's the difference between varargs[T] and openArray[T]?

• mogu (orginal) [2015-03-24T03:44:45+01:00] view original

  After I'v read tutorials and manuals, i can't find more instances about openArray. Could someone tells? Thanks!

---

• jboy (orginal) [2015-03-24T07:16:44+01:00] view original

  Hi @mogu, my understanding of the difference is this:

  • openArray[T] is a form of duck-typing specifically for proc/macro parameters. A single openArray[T] parameter can accept a single argument of either array[AnyIndexRange, T] or seq[T].
  • varargs[T] is another type defined specifically for proc/macro parameters. A single varargs[T] parameter can accept any number (ie, zero, one or more) of arguments of type T, enabling the proc/macro to accept a variable number of parameters (like printf in C).

  Does this match your own understanding?

---

• mogu (orginal) [2015-03-24T09:28:43+01:00] view original

  Thanks very much. Do you mean openArray is an efficient way to accept both array and seq?

---

• jboy (orginal) [2015-03-24T09:48:04+01:00] view original

  Hm, I wouldn't know about "efficient" (in the sense of computational efficiency).

  I'd say "convenient" and "consistent". Whenever you write a proc that reads (but doesn't need to create, update or delete) elements in an abstract sequence (which might be implemented using either an array or a seq), you can define a single form of the proc that accepts an openArray rather than duplicating everything for array and seq.

  If you skim through the system module, you can see this idiom used frequently. For example:

  • len
  • contains
  • each

---

• mogu (orginal) [2015-03-24T10:37:42+01:00] view original

  Thanks for your help! Finally, i got it. ;)

---