Re: [Caml-list] Using %identity for casting types

[jmarant@nerim.net (Jérôme Marant)]

Jacques Garrigue <garrigue@kurims.kyoto-u.ac.jp> writes:

> Well, not really, but if you're interfacing with C++, it's not more
> dangerous to do the cast in ocaml than in C++ (except if you use
> rtti).
>
> The above idiom is equivalent to
>
>     let unsafe_cast : 'a obj -> 'b obj = Obj.magic
>
> It may be more efficient, as the compiler knows that unsafe_cast is
> the identity, and can discard it. No code is generated.
>
> I also tend to prefer it because it makes clear the need to properly
> write types: such casts only make sense at a precise type, while
> Obj.magic is 'a -> 'b, which allows too much.
>
> And, as always, only use unsafe casts for non-ocaml data.
> Ocaml datatypes are expressive enough that you don't need unsafe
> casts for them.

Thanks a lot.

Cheers,

-- 
Jérôme Marant

http://marant.org
              
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