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Date: Fri, 17 Jan 2014 14:56:12 +0100
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To: Nicolas Braud-Santoni <nicolas.braudsantoni@gmail.com>, 
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Subject: Re: [Caml-list] How much optimized is the 'a option type ?


Le 17/01/2014 14:46, Nicolas Braud-Santoni a écrit :
> On 17/01/2014 12:23, Jonathan Kimmitt wrote:
>> In my humble opinion the main purpose of Some _ | None is to avoid the
>> requirement for a nil pointer in OCaml. If an external function wants to
>> return nil in order to indicate, for example that a certain resource is not
>> available, it can return None instead and this prevents dereferencing a nil
>> pointer in OCaml because the None cannot be dereferenced.
> Yes.
> This doesn't forbid the compiler from representing 'a option values as
> pointers.
> Indeed, the type system already enforces that the None case is handled
> and the representation of None and Some _ do not matter.
>
> That said, I agree with Gabriel Scherer : adding optimizations specific
> to 'a option might refrain people wanting to switch to more appropriate
> datatypes.
> However, would is be possible to “optimize away” all types of the form
> “type 'a t = X of 'a | A | B | ...” (with at most one non-constant
> constructor) ?
> Would it be worth doing ?

This won't work when used with 'a = another type with constant constructors.
And what about 'a 'a t?

Sticking to a uniform representation prevents a lot of problem.

> Kind regards,
> Nicolas