Re: [Caml-list] Design advice

[William Lovas <wlovas@stwing.upenn.edu>]

On Sat, Sep 28, 2002 at 03:55:43AM -0700, Chris Hecker wrote:
> >type, but now I have to convert this to an integer whenever I want to
> >use the player number as an index.
> 
> type suit = Spades | Hearts | Diamonds | Clubs
> 
> let suit_to_int (s : suit) =
>         assert (Obj.is_int (Obj.repr s));
>         ((Obj.magic s) : int)
> 
> The assert will catch it if you add variables to one of the constructors 
> and then call this.  This uses magic, which is bad, but it alleviates you 
> having to type the variant constructors again and possibly make an error in 
> the assocation with the int, which is good.  Pick your poison.

Wouldn't it be safer to just do something like:

    let suit_to_int = function
      | Spades   -> 0
      | Hearts   -> 1
      | Diamonds -> 2
      | Clubs    -> 3

?  You only have to type it once, and if you change the constructors
around, it won't even compile.  Plus it gives you control over which
int a suit corresponds to -- i doubt you can get any sort of guarantee
if you use Obj.magic.

William
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