Re: [Caml-list] const equivalent for mutable types?

[Jon Harrop <jon@jdh30.plus.com>]

On Saturday 31 July 2004 11:34, Markus Mottl wrote:
> ...
>   val incr : (int, [> `W ]) t -> unit
>   val decr : (int, [> `W ]) t -> unit

Should these both be [`R|`W]?

> The phantom variable is 'rw.  When creating references, it can be any
> of `R (for reading) and `T (for writing).

Do you mean `W for writing?

That's very interesting. So a phantom type is a type which you stick in to 
dupe the type system into doing something for you? Is there a good reference 
on those? I seem to remember a thread about their utility in porting the STL 
to ocaml but that was before I had ever used OCaml...

And this const-alternative is useful when dealing with large records which 
have mostly constant but some mutable entries because handling such records 
invokes a lot of copying? But, say, arrays are passed by reference so this 
wouldn't provide much of a performance advantage, is that right? 
Incidentally, does anyone have a functional array implementation (which 
doesn't suck ;-)?

Cheers,
Jon.

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