gistfile1.nim

proc initT (some: var string) = some = newStringOfCap(64)
proc initT [T] (some: var seq[T]) = newSeq[T](some, 0)

template filterIt*(seq1, pred: expr): expr {.immediate.} =
  ## Returns a new sequence with all the items that fulfilled the predicate.
  ##
  ## Unlike the `proc` version, the predicate needs to be an expression using
  ## the ``it`` variable for testing, like: ``filterIt("abcxyz", it == 'x')``.
  ## Example:
  ##
  ## .. code-block::
  ##    let
  ##      temperatures = @[-272.15, -2.0, 24.5, 44.31, 99.9, -113.44]
  ##      acceptable = filterIt(temperatures, it < 50 and it > -10)
  ##      notAcceptable = filterIt(temperatures, it > 50 or it < -10)
  ##    assert acceptable == @[-2.0, 24.5, 44.31]
  ##    assert notAcceptable == @[-272.15, 99.9, -113.44]
  bind initT
  var result {.gensym.}: type(seq1)
  initT result
  for it {.inject.} in items(seq1):
    if pred: result.add(it)
  result


var s = "abc"
echo s.filterIt(it < 'c')
var s2 = @['a','b','c']
echo s2.filterIt(it < 'c')