PHP assign value to $this

Question

Basically what I'm trying to achieve is to make the object reference another object of the same class - from inside of a method. It'd be perfect if the following would work:

$this = new self;

But one cannot reassign $this in php.

I of course know, I can return another object from the method and use that, so please do not advise that. The question is:

How can I make $this to be a clone of another object of the same class?

or more specifically,

I want an object to revert to a specific state that was previously saved.

---

EDIT: some examples where this might be useful.

Say you have an Url object that accepts controller, action and lots more things. You are going to have it fetch a lot of links with the same, say, controller and action, but other properties will differ. I instantiate the object with the common parameters, call a method for it to save its state which it reverts to after outputting a link (IOW after __toString method).

$defaultPath = Url::factory('controller','action1')->extraParams('status',0)->save();

echo $defaultPath->action('action2'); // this has action2 as action and a status 0 as extra params
echo $defaultPath->extraParams('status',2); // this has action1 as action and 2 as status

Another use is I have a CRUD table and I have to configure each column as an object I pass to the main table object. After passing the column I launch a reset method on the column, so I can have code like the following:

    $column->field = 'layouts_id';
    $column->value = $layoutId;
    $dbInput->addColumn($column);

    $column->field = 'pages_id';
    $column->value = $pagesId;
    $dbInput->addColumn($column);

In both situations I save a lot of code and confusion, don't you think?

Answer 1

I see a huge problem with what you're intending:

If you found a way to reassign $this, how do you make sure, that anybody using your class knows how it behaves? While I admit, that it's kinda interesting to do

$column->field = 'layouts_id';
$column->value = $layoutId;
$dbInput->addColumn($column);

$column->field = 'pages_id';
$column->value = $pagesId;
$dbInput->addColumn($column);

What happens, if I need $column twice?

$column->field = 'layouts_id';
$column->value = $layoutId;
$dbInput->addColumn($column);
// log my value
$logger->log($column); // oops, it's empty

...

You would break the expected behaviour and imho make it extremely hard to grasp your code.

---

But to give some ideas on how to still achieve the aforementioned behaviour:

// clone when passing on
$column->field = 'value_id';
$column->value = $value;
$dbInput->addColumn(clone $column);

// manually (re-)create a new object based on an older
$column->field = 'value_id';
$column->value = $value;
$dbInput->addColumn(new Column($column));

---

Otherwise the reset() method also sounds feasible:

class Column() {

    public function reset() {
        $this->field = 'standard field id';
        $this->value = 'standard field value';
    }

    public function __construct() {
        $this->reset();
    }

}

This way you could use it like so:

// manually (re-)create a new object based on an older
$column->field = 'value_id';
$column->value = $value;
$dbInput->addColumn($column);
$column->reset();

---

To overcome the problem of specifying the default values twice (untested):

class Column() {

    public $field = 'standard field id';
    public $value = 'standard field value';

    // keep a static object for resetting
    private static $__blueprint = null;

    public function reset() {
        foreach (self :: $__blueprint as $k => $v)
            $this->$k = $v;
    }

    public function __construct() {
        if (!isset(self :: $__blueprint))
            self :: $__blueprint = clone $this;
    }

}