Re: [Ocaml-lib-devel] Array interface

[Eric C. C. <ec...@cm...>]

On Fri, Jun 20, 2003 at 03:58:38PM -0500, Brian Hurt wrote:
> Unless I'm missing something (which is possible), there are three possible
> implementations of Dynarray that I can see working:
> 
> 1) Have the internal array be a 'a option array, and not a 'a array as it 
> is currently. [...]
> 2) Use the null value kludge. [...]
> 3) Write in C, leaving floats unboxed. [...]

I'm probably missing some essential context, but what is wrong with
the simple approach of using a mutable 'a array that gets replaced
with a bigger one when you try to set an element beyond its current
length?

Something like the following:

type 'a t =
    { mutable data : 'a array;
      mutable length : int }

let make n v = { data = Array.make n v; length = n }

let empty () = { data = [||]; length = 0 }

let length a = a.length

let get a i =
  if i < a.length then
    a.data.(i)
  else
    raise (Invalid_argument "Dynarray.get")

let set a i v =
  if i >= a.length then
    begin
      if i >= Array.length a.data then
	begin
	  let n = Array.length a.data in
	  let newlen = max (i+1) (2*n) in
	  let newdata = Array.make newlen v in
	  Array.blit a.data 0 newdata 0 n;
	  a.data <- newdata
	end;
      a.length <- i + 1
    end;
  a.data.(i) <- v

-- 
Eric C. Cooper          e c c @ c m u . e d u