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Date: Sat, 5 Jan 2013 08:39:15 -0500
To: "ivan.enderlin@hoa-project.net" <ivan.enderlin@hoa-project.net>
Subject: Re: [PHP-DEV] Ruby's symbols
From: tom@punkave.com (Tom Boutell)

If symbols could use the sign bit or otherwise distinguish from typical inte=
ger keys one would have some hope of meaningful debugging output. I don't th=
ink it makes sense to mix integer keys and symbol keys but being able to dif=
ferentiate them for debugging purposes would be great. However since php arr=
ays are sparse anyway is there much of a win from integer keys in the first p=
lace?

Sent from my iPhone

On Jan 5, 2013, at 6:28 AM, "Ivan Enderlin @ Hoa" <ivan.enderlin@hoa-project=
.net> wrote:

> Hi :-),
>=20
> Nice proposal but I have few questions and remarks.
>=20
> My first question is how to delete symbols? I don't know if it is useful o=
r not. We should discuss about that. Is `unset(:foo)` enough? How are they h=
andled by the GC?
>=20
> Another question is: where are we able to use symbols? Is it allowed to wr=
ite `const FOO =3D :bar` for example? Or in a default argument value: `publi=
c function f ( $x =3D :foo ) { =E2=80=A6 }`?
>=20
> What kind of (arithmetical) operations are allowed on symbols?
>=20
> You proposed to represent symbols as integers. Could it create conflicts? =
For example: `$foo =3D [0 =3D> 'bar', :baz =3D> 'qux']`. What happens if `:b=
az` is set to 0?
>=20
> Finally, if my memory is good, a few months ago, some patches were updatin=
g =E2=80=9Cconstant strings=E2=80=9D performances by representing them as =E2=
=80=9Cbuffers=E2=80=9D/=E2=80=9Cconstants=E2=80=9D internally, no? Maybe I'm=
 wrong, but it could be a middle-way solution if it is not yet implemented (=
especially since we have strings dereferencing, implementation could be ease=
).
>=20
> My two cents :-).
> Best regards.
>=20
>=20
>=20
>=20
> On 05/01/13 15:07, Nikita Nefedov wrote:
>> I know I shouldn't write "Ruby" in the subject of a letter for php-intern=
als ML, but... Just wanted to ask, is anybody interested in this feature in P=
HP?
>> You can read about it here: http://www.randomhacks.net/articles/2007/01/2=
0/13-ways-of-looking-at-a-ruby-symbol
>>=20
>> It can be implemented in PHP as a HashTable where key would be strings an=
d values would be unique identifiers (just incrementing long, can be tracked=
 with nNextFreeElement).
>>=20
>> How it would work in userland?
>>=20
>> If it would be proposal, I would divide it on two different (competitive)=
 proposals:
>>=20
>> First, we could implement it so symbol expression would return an associa=
ted integer.
>> (note that symbols are most often used as hash keys in ruby so my example=
s are relying on it)
>> Example:
>> $foo =3D array();
>> $foo[:bar] =3D "qwerty";
>>=20
>> var_dump($foo);
>> // array(1) {
>> //  [0] =3D>
>> //  string(6) "qwerty"
>> //}
>>=20
>> var_dump(:bar); // int(0)
>>=20
>> var_dump(:some_new_symbol); // int(1)
>>=20
>> This is the easiest way, and I can implement it. But, it would be hard to=
 debug.
>>=20
>> The second way - we can implement it as a new variable type, and the main=
 thing is that arrays will be able to take variables of symbol type as keys,=
 I know it sounds scary but it's not so hard actually.
>> I will drop the part about new variable type, the main thing is how HashT=
ables could work with symbols as keys.
>> We could change the type of nKeyLength (in Bucket) to signed integer (now=
 it's unsigned, I don't think we will miss something from that) and use it a=
s a flag: if it's -1 (less than zero) - then we know the symbol was used as a=
 key, there will be filled bucket.h member with a symbol identifier.
>> That way the above code will evaluate so:
>> $foo =3D array();
>> $foo[:bar] =3D "qwerty";
>>=20
>> var_dump($foo);
>> // array(1) {
>> //  [:bar] =3D>
>> //  string(6) "qwerty"
>> //}
>>=20
>> var_dump(:bar); // symbol(:bar)
>>=20
>> var_dump(:some_new_symbol); // symbol(:some_new_symbol)
>>=20
>> To make it clear, when retrieving an element by symbol from array, these s=
teps will be needed:
>> 1. Get symbol identifier (ulong)
>> 2. Get elements from array where bucket.h equals to this identifier
>> 3. Iterate over those elements and find the one that has nKeyLength =3D=3D=
 -1
>> (actually we will iterate over pNext/pLast elements)
>>=20
>>=20
>> What symbols can give:
>> 1. More convenient way to use it almost everywhere as a replacement for s=
trings and sometimes for constants. There's a lot of code that uses arrays a=
s a parameter-stores. For example, here's how you usually define a form in S=
ymfony2:
>>        $builder
>>            ->add('title', 'text', array(
>>                'label' =3D> 'Album title'
>>            ))
>>            ->add('title_alias', 'text', array(
>>                'label' =3D> 'Album alias',
>>                'required' =3D> false,
>>                'property_path' =3D> 'properties.titleAlias'
>>            ))
>>            ->add('comment', 'text', array(
>>                'label' =3D> 'Comment',
>>                'required' =3D> false,
>>                'property_path' =3D> 'properties.comment'
>>            ))
>>            ->add('labels', 'text', array(
>>                'label' =3D> 'Musical labels',
>>                'required' =3D> false,
>>                'property_path' =3D> 'properties.labels'
>>            ))
>>            ->add('language', 'text', array(
>>                'required' =3D> false,
>>                'property_path' =3D> 'properties.language'
>>            ))
>> It could be improved this way:
>>        $builder
>>            ->add('title', :text, array(
>>                :label =3D> 'Album title'
>>            ))
>>            ->add('title_alias', :text, array(
>>                :label =3D> 'Album alias',
>>                :required =3D> false,
>>                :property_path =3D> 'properties.titleAlias'
>>            ))
>>            ->add('comment', :text, array(
>>                :label =3D> 'Comment',
>>                :required =3D> false,
>>                :property_path =3D> 'properties.comment'
>>            ))
>>            ->add('labels', :text, array(
>>                :label =3D> 'Musical labels',
>>                :required =3D> false,
>>                :property_path =3D> 'properties.labels'
>>            ))
>>            ->add('language', :text, array(
>>                :required =3D> false,
>>                :property_path =3D> 'properties.language'
>>            ))
>> 2. Memory usage reduction. AFAIK, there's a lot of cases like the above a=
nd the use of symbols would affect on memory usage significantly.
>> 3. Memory leaks. Symbols can't be just garbage collected as, for example z=
vals, it's not possible. But we can do it for every request, so I don't thin=
k it would be problem.
>> 4. Autocompletion from IDEs.
>>=20
>> PS I don't want to call it "proposal", despite the fact that this is actu=
ally a proposal, I'm just not sure it can go as a proposal.
>>=20
>=20
> --=20
> Ivan Enderlin
> Developer of Hoa
> http://hoa.42/ or http://hoa-project.net/
>=20
> PhD. student at DISC/Femto-ST (Vesontio) and INRIA (Cassis)
> http://disc.univ-fcomte.fr/ and http://www.inria.fr/
>=20
> Member of HTML and WebApps Working Group of W3C
> http://w3.org/
>=20
>=20
>=20
> --=20
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>=20