moves.nim

when defined(nimOpMove):

  proc `=move`[T](x, y: var seq[T]) =
    mixin `=destroy`
    if a.p != b.p:
      var a = cast[ptr NimSeqV2[T]](addr x)
      var b = cast[ptr NimSeqV2[T]](addr y)
      if a.p != nil: `=destroy`(x)
      a.len = b.len
      a.p = b.p
      # p is stolen, so afterwards it must be nil 
      b.p = nil

else:

  proc `=sink`[T](x: var seq[T]; y: seq[T]) =
    mixin `=destroy`
    var a = cast[ptr NimSeqV2[T]](addr x)
    var b = cast[ptr NimSeqV2[T]](unsafeAddr y)
    if a.p != nil and a.p != b.p:
      `=destroy`(x)
    a.len = b.len
    a.p = b.p