Everything

php

$var::$static

php.internals

Bart de Boer

19 years ago

Hi all,

I'd like to be able to do the following:


<?php

class Base {

public static $var = 'hello';

public function someFunc() {
echo self::$var; // Currently maps to Base::$var
echo $this::$var; // Should map to Child::$var
}

}

class Child extends Base {

public static $var = 'hello';

}

$class = 'Child';

$obj = new $class(); // This works.

echo $class::$var; // This doesn't. Should map to Child::$var


?>


...in other words: I'd like to be able to access static class variables
from inside an instance of the Base and/or Child classes. I'd also like
to be able to access them dynamically. ($className::$variable)

The only way to do this at the moment (to my knowledge at least) is to
create functions in the Child class that returns its static variables.
The downside of this is that those functions most likely will be very
common (in my case they are) and should therefore belong in the base
class. Hence: $this::$variable

At the moment there is no way to access static variables from outside of
the class dynamically. As a workaround for this I'm currently creating a
temporary instance (new $type()) to access them dynamically with a
__get() function in all the derived child classes.

There are ways to do it with class constants and the constant functions.
But it's not very elegant and class constants can't hold arrays and/or
objects.

I have no idea what the implications would be. Just thought it would be
a nice addition to the language. :) Hope I didn't overlook some existing
PHP feature that already allows me to do this. :|


Cheers,

Bart de Boer

Marco Kaiser

19 years ago

Hi,

this doesnt work because static vars are bound to his class and are not
inherited by a child class.
maybe this would be work with php6 or a other 5.x version.
(Same behavior like the singleton pattern getInstance() abstract class
stuff)

-- Marco

Bart de Boer

19 years ago

I understand... My suggestion would be to map $this to the class name
(of the current instance) if the Scope Resolution Operator '::' is used...


Marco Kaiser wrote:

Bart de Boer

19 years ago

I seem to have been a bit too hasty with my previous reply... You meant
it wouldn't be able to access the static vars of the inherited Base
class?... I think that's a different feature regarding the static access
mechanism currently already in place... I'm only suggesting the ability
to reference classes dynamically some way...

-- Bart


Marco Kaiser wrote:

Arnold Daniels

19 years ago

Hi,

I agree that $this::$var isn't really logical, since $this is an object
and not a class name. But I do not see why $class::$var shouldn't work,
or $class::$method() for that method. You can also do $function().

Also I want to suggest that brackets can be used more freely. Currently
you can use ${$group . '_myvar'}, but you can't do the same for
functions and classes. It would be great if you could use {$group . '_'
. $fn}() and {get_class($this)}::$var.

The way to solve this problems right now is to use eval('return ' .
get_class($this) . '::$var;') for getting the value. Getting a reference
to the variable to set it, is even more messy. You need to do something
like eval('$cvar =& ' . get_class($this) . '::$var;'); $cvar = 'bye';.

Anyway, it is not so nice, but doable in user space fairly easily. So I
don't see why anything needs to be added in PHP 5. It would be nice to
have a better method in PHP 6 though.

From Holland with love,
Arnold


Bart de Boer wrote:

Greg Beaver

19 years ago

Arnold Daniels wrote:

> Hi,
>
> I agree that $this::$var isn't really logical, since $this is an object
> and not a class name. But I do not see why $class::$var shouldn't work,
> or $class::$method() for that method. You can also do $function().
>
> Also I want to suggest that brackets can be used more freely. Currently
> you can use ${$group . '_myvar'}, but you can't do the same for
> functions and classes. It would be great if you could use {$group . '_'
> . $fn}() and {get_class($this)}::$var.
>
> The way to solve this problems right now is to use eval('return ' .
> get_class($this) . '::$var;') for getting the value. Getting a reference
> to the variable to set it, is even more messy. You need to do something
> like eval('$cvar =& ' . get_class($this) . '::$var;'); $cvar = 'bye';.
>
> Anyway, it is not so nice, but doable in user space fairly easily. So I
> don't see why anything needs to be added in PHP 5. It would be nice to
> have a better method in PHP 6 though.
>
> From Holland with love,
> Arnold

Hi Arnold,

<?php
$a = $group . '_' . $fn;
$a();
?>

As for get_class($this)::$var it pays to search the mailing list
archives.  the static:: keyword is being using in PHP 6 to do exactly
what you want from within a class.  Outside of a class, $var::$value
doesn't work yet, but the implementation of static may make it possible
to implement $var::$value as well.

Greg

P.S. The list archives are http://marc.info/?l=php-dev and are searchable

Arnold Daniels

19 years ago

Hi again,

I'm aware that you can do `$a = $group . '_' . $fn; $a();`, but you can
do `$b = $group . '_' . $var; echo $$b;` as well as `echo ${$group . '_'
. $var}`. It's a mater of style, not if there is any way to get it done.

Yes I've read about 'static::' some time ago, but forgot about it.
Thanks for pointing it out. I (unfortunately) took that as an example,
but it wasn't the case I wanted to make.

To my opinion, the ease with which you can use output of an expression
to be used as name of a variable is wonderful. The code is so much
clearer than when you have to create all kind of temporary variables
and/or use eval. I think it is unfortunate that the same logic isn't
available for functions and classes.

Best regards,
Arnold



Gregory Beaver wrote:

Daniel Convissor

19 years ago

On Sat, May 26, 2007 at 01:50:04PM +0200, Bart de Boer wrote:

>
> class Base {
> 	public static $var = 'hello';
>
> 	public function someFunc() {
> 		echo self::$var; // Currently maps to Base::$var
> 		echo $this::$var; // Should map to Child::$var

Here, and throughout the example, you're mixing static and object
contexts.  You need to pick one or the other and stick to it.  If you
really want static, use child::$var.

--Dan

--
T H E   A N A L Y S I S   A N D   S O L U T I O N S   C O M P A N Y
data intensive web and database programming
http://www.AnalysisAndSolutions.com/
4015 7th Ave #4, Brooklyn NY 11232  v: 718-854-0335 f: 718-854-0409

Daniel Convissor

19 years ago

On Sun, May 27, 2007 at 11:35:04AM -0400, Daniel Convissor wrote:

> On Sat, May 26, 2007 at 01:50:04PM +0200, Bart de Boer wrote:
> >
> > class Base {
> > 	public static $var = 'hello';
> >
> > 	public function someFunc() {
> > 		echo self::$var; // Currently maps to Base::$var
> > 		echo $this::$var; // Should map to Child::$var
>
> Here, and throughout the example, you're mixing static and object
> contexts.  You need to pick one or the other and stick to it.  If you
> really want static, use child::$var.

Though that's only working because the child class' name is "Child". :/

--Dan

--
T H E   A N A L Y S I S   A N D   S O L U T I O N S   C O M P A N Y
data intensive web and database programming
http://www.AnalysisAndSolutions.com/
4015 7th Ave #4, Brooklyn NY 11232  v: 718-854-0335 f: 718-854-0409

Etienne Kneuss

19 years ago

Hi,

Bart de Boer wrote:

> $class = 'Child';
>
> $obj = new $class(); // This works.
>
> echo $class::$var; // This doesn't. Should map to Child::$var
>
>

This feature request was already brought up a couple of weeks/months
ago, please consider:

http://news.php.net/php.internals/29067

Regards

--
Etienne Kneuss
http://www.colder.ch
colder@php.net

Men never do evil so completely and cheerfully as
when they do it from a religious conviction.
-- Pascal