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8779 :: real type of openArray?

• oyster (orginal) [2022-01-06T02:09:37+01:00] view original

  the following code says

  x.type = seq[string]
  x.type is seq = true
  y.type = array[0..3, string]
  y.type is array = true
  
  
  in fn
  x.type = openArray[string]
  x.type is seq = false
  y.type = openArray[string]
  y.type is array = false
  
  
  Run

  but how to get

  
  x.type = seq[string]
  x.type is seq = true
  y.type = array[0..3, string]
  y.type is array = true
  
  in fn
  x.type = seq[string]
  x.type is seq = true
  y.type = array[0..3, string]
  y.type is array = true
  
  Run

  thanks

  import sugar
  proc fn(x: openArray[string], y: openArray[string]) =
      echo "in fn"
      dump x.type
      dump x.type is seq
      
      dump y.type
      dump y.type is array
  
  var
      x = @["1", "2", "3"]
      y = ["4", "5", "6", "7"]
  
  dump x.type
  dump x.type is seq
  
  dump y.type
  dump y.type is array
  
  echo "\n"
  
  fn(x, y)
  Run

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• doofenstein (orginal) [2022-01-06T02:16:01+01:00] view original

  openArray is not a type class, a proc which accepts an openArray (and doesn't have anything else which could make it generic) is not generic. Instead it's a type to which seq and array implicitly convert, the original type is lost, the same way after converting a float to an int you can't recover the float value.

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• ElegantBeef (orginal) [2022-01-06T02:17:04+01:00] view original

  openarray's type is openarray, sequences/array's can implicitly convert to a non typeclassed openarray parameter, internally an openarray is a ptr T, len which is important for allowing iteration over any array. Without openarray applying logic over array[-10..0, int], array[bool, int] and array[10, int] would require manually handling. What happens is when you call something using openarray it passes yourCollection[0].addr, yourCollection.len in a hidden conversion to the proc.

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