Re: [Caml-list] How to do this properly with OCaml?

[Brian Hurt <bhurt@spnz.org>]

On Mon, 25 Jul 2005, Stephane Glondu wrote:

> Brian Hurt wrote:
>> let get arr idx =
>>     if (idx < 0) || (idx > arr.len) then
>>        invalid_arg "get_arr"
>>     else
>>        arr.data.(idx)
>> ;;
>
> Maybe:
>
> let get arr idx =
>    if (idx < 0) || (idx > arr.len) then
>       invalid_arg "get_arr"
>    else
>       match arr.data.(idx) with None -> assert false | Some a -> a
> ;;
>
> would be better...

Duh!  Yeah- thinko there.  That's what I meant.

> Maybe storing the arr.data's length in the record would be better...

Not really.  Array.length is a pretty efficient routine- it gets inline to 
a mov, shift, and mask IIRC.

> But skaller already argued that he didn't like this approach.

Yep.  His argument is "It's impossible to implement cleanly, except for 
the obvious solution, which I hate."  OK, so it's not very efficient for 
integers.  Hey, why stop there?  If it's an array of chars or bools, using 
whole words to store individual members is inefficient!  We should only 
store the bytes or individual bits.  For anything much larger than ints, 
this actually isn't that inefficient.

Brian