Re: [Caml-list] How much optimized is the 'a option type ?

[Julien Blond <julien.blond@gmail.com>]

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> An option value always takes two words: one for the header, and then
either a pointer or a word that means "None".

No. From the reference manual § 19.3.4 :

type 'a option = None           (* Val_int(0), i.e. just an integer value =
1 word *)
                     | Some of 'a   (* block of size 1 = [(header = 1 word)
+ (1 field = 1 word)] = 2 words *)


2014/1/17 David House <dhouse@janestreet.com>

> It behaves identically to that type.
>
> It is just like any other sum type. However, due to the way that sum types
> are represented in memory, it is not that inefficient. The only thing that
> makes it less efficient than a C pointer is the header block (necessary for
> the GC). An option value always takes two words: one for the header, and
> then either a pointer or a word that means "None".
>
>
> On 17 January 2014 07:35, Damien Guichard <alphablock@orange.fr> wrote:
>
>> Hello,
>>
>> Compared to the code :
>>
>> type 'a option = None | Some of 'a
>>
>> How do an 'a option value performs ?
>> Any allocation saved ?
>> Any indirection removed ?
>>
>> Is 'a option just like any sum type ?
>> Or is 'a option more like an ANSI C pointer type ?
>>
>> Regards,
>>
>> Damien Guichard
>>
>>
>>
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>
>

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