Edit report at https://bugs.php.net/bug.php?id=46506&edit=1
ID: 46506
Comment by: info at strictcoding dot co dot uk
Reported by: glideraerobatics at hotmail dot com
Summary: readonly attribute for (public) class variables
Status: Open
Type: Feature/Change Request
Package: *General Issues
PHP Version: 5.4
Block user comment: N
Private report: N
New Comment:
+1 for this awesome feature. Any reviews from the PHP team?
Previous Comments:
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[2012-09-18 21:53:20] mat dot barrie at gmail dot com
As a point of interest, the C# readonly keyword mentioned actually does not
protect exposed classes from being modified, it prevents assignment. So from
your example if you duplicate the C# behaviour, this is what it actually would
work like this, which I don't think is what you're asking for:
--
$count = count($parent->children); // You can do this
$name = $parent->children[0]; // You can even do this
$parent->children[0] = "BILLY"; // You can still do this
$parent->children[] = "BOB"; // And you can still even do this
$parent->children = NULL; // But not this
unset($parent->children); // Or this
--
A readonly attribute probably isn't what's needed here (after all, you're not
actually asking for a property that can be made readonly) but instead if the
protection level could be defined on the getter and setter independently, so
that set could be defined as private and get as public. __get and __set sort
of
do this, but they're useless if you're serialising, hurt performance, and
unless
I'm missing something you can't add phpDoc comments to the exposed pseudo-
properties.
------------------------------------------------------------------------
[2012-01-25 08:11:40] glideraerobatics at hotmail dot com
Changed affected PHP version.
------------------------------------------------------------------------
[2012-01-24 23:12:32] luke at cywh dot com
I just want the "readonly" keyword to protect a property from being written to
from the outside. I still want to write to the property from within the class.
Here's a simple example of how it could be used:
class Parent
{
readonly public $children = array();
public function addChild($childName)
{
$this->children[] = ucwords(strtolower($childName));
}
}
$parent = new Parent;
$parent->addChild("billy");
$count = count($parent->children); // You can do this
print "Parent has $count children\n";
$name = $parent->children[0]; // You can even do this
print "Parent's first child's name is $name\n";
$parent->children[0] = "BILLY"; // But you can't do this
$parent->children[] = "BOB"; // Or this
$parent->children = NULL; // Or this
unset($parent->children); // Or this
The above example frees you from having to do this:
class Parent
{
protected $children = array();
public function addChild($childName)
{
$this->children[] = ucwords(strtolower($childName));
}
public function hasChild($index)
{
return isset($this->children[$index]);
}
public function getChild($index)
{
return $this->children[$index];
}
public function childCount()
{
return count($this->children);
}
}
I've had to write MANY classes like this. The has/isset, get, and count
functions are virtually all the same.
Some people have even resorted to using __get and __set:
http://stackoverflow.com/questions/402215/php-readonly-properties
The __get and __set magic functions are slow, so much so you're better off
making your own getters and setters, which is multiplied by the number of
properties you need like this in the class.
I would recommend the following definitions:
readonly public = read for public, write for protected
readonly protected = read for protected, write for private
I think this should satisfy most cases.
------------------------------------------------------------------------
[2009-07-12 13:27:08] mickael at lupusmic dot org
I guess the readonly keyword in C# is wrong. It hasn't to disallow variance of
the attribute, but the setting from outside the object. Readonly is opposite to
constness of a variable. For example, DOMDocument::doctype isn't constant.
What you think about, it's a dynamic const attribute, in opposite to static one.
So said, a readonly is like a const attribute, but isn't. And it doesn't
deserve a scope qualifier, it can only be public.
For example :
class thing
{
readonly $status = 'instantiation' ;
public function __construct()
{
// do init stuff
$this->status = 'instantiate' ;
}
public function invalidate()
{
// do stuf
$this->status = 'invalid' ;
}
}
// Usage
$o = new thing ;
echo $o->status ; // display 'instantiation'
$o->status = 'forced' ; // throw an error E_FATAL
$o->invalidate() ; // do stuff then set readonly status attribute
------------------------------------------------------------------------
[2008-11-06 14:11:42] glideraerobatics at hotmail dot com
Description:
------------
Here is a description of this feature in C#:
http://blog.paranoidferret.com/index.php/2007/09/12/csharp-tutorial-the-readonly-keyword/
In a nutshell it allows you to create classes with public variables that are
readonly and can only be written to / initialized by the contructor of the
class itself.
This allows the creation of simple objects without having using accessor
methods to protect the internal data that was validated and initialized during
construction from corruption.
Note: bug http://bugs.php.net/bug.php?id=39467 is about a similar problem but
the proposed solution is not quite right.
Reproduce code:
---------------
class Person
{
public readonly $name = null;
public readonly $age = null;
public readonly $weight = null;
public function __construct($name, $age, $weight) {
{
if (!isAgeToWeightRatioSane($age, $weight)) {
throw new InvalidArgumentException("Invalid age to weight ratio: $age :
$weight");
}
// TODO: other sanity checks here.
$this->name = $name;
$this->age = $age;
$this->weight = $weight;
}
}
$person = new Person('Joe', 22, 100);
$person->age = 33; // throws a yet to be named exception
------------------------------------------------------------------------
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Edit this bug report at https://bugs.php.net/bug.php?id=46506&edit=1
