I know I shouldn't write "Ruby" in the subject of a letter for
php-internals ML, but... Just wanted to ask, is anybody interested in this
feature in PHP?
You can read about it here:
http://www.randomhacks.net/articles/2007/01/20/13-ways-of-looking-at-a-ruby-symbol
It can be implemented in PHP as a HashTable where key would be strings and
values would be unique identifiers (just incrementing long, can be tracked
with nNextFreeElement).
How it would work in userland?
If it would be proposal, I would divide it on two different (competitive)
proposals:
First, we could implement it so symbol expression would return an
associated integer.
(note that symbols are most often used as hash keys in ruby so my examples
are relying on it)
Example:
$foo = array();
$foo[:bar] = "qwerty";
var_dump($foo);
// array(1) {
// [0] =>
// string(6) "qwerty"
//}
var_dump(:bar); // int(0)
var_dump(:some_new_symbol); // int(1)
This is the easiest way, and I can implement it. But, it would be hard to
debug.
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
HashTables 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
as 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 = array();
$foo[:bar] = "qwerty";
var_dump($foo);
// array(1) {
// [:bar] =>
// string(6) "qwerty"
//}
var_dump(:bar); // symbol(:bar)
var_dump(:some_new_symbol); // symbol(:some_new_symbol)
To make it clear, when retrieving an element by symbol from array, these
steps 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 == -1
(actually we will iterate over pNext/pLast elements)
What symbols can give:
1. More convenient way to use it almost everywhere as a replacement for
strings and sometimes for constants. There's a lot of code that uses
arrays as a parameter-stores. For example, here's how you usually define a
form in Symfony2:
$builder
->add('title', 'text', array(
'label' => 'Album title'
))
->add('title_alias', 'text', array(
'label' => 'Album alias',
'required' => false,
'property_path' => 'properties.titleAlias'
))
->add('comment', 'text', array(
'label' => 'Comment',
'required' => false,
'property_path' => 'properties.comment'
))
->add('labels', 'text', array(
'label' => 'Musical labels',
'required' => false,
'property_path' => 'properties.labels'
))
->add('language', 'text', array(
'required' => false,
'property_path' => 'properties.language'
))
It could be improved this way:
$builder
->add('title', :text, array(
:label => 'Album title'
))
->add('title_alias', :text, array(
:label => 'Album alias',
:required => false,
:property_path => 'properties.titleAlias'
))
->add('comment', :text, array(
:label => 'Comment',
:required => false,
:property_path => 'properties.comment'
))
->add('labels', :text, array(
:label => 'Musical labels',
:required => false,
:property_path => 'properties.labels'
))
->add('language', :text, array(
:required => false,
:property_path => 'properties.language'
))
2. Memory usage reduction. AFAIK, there's a lot of cases like the above
and the use of symbols would affect on memory usage significantly.
3. Memory leaks. Symbols can't be just garbage collected as, for example
zvals, it's not possible. But we can do it for every request, so I don't
think it would be problem.
4. Autocompletion from IDEs.
PS I don't want to call it "proposal", despite the fact that this is
actually a proposal, I'm just not sure it can go as a proposal.
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