Dynamically add a private property to an object

问题:

I have a class:

class Foo {
    // Accept an assoc array and appends its indexes to the object as property
    public function extend($values){
        foreach($values as $var=>$value){
            if(!isset($this->$var))
                $this->$var = $value;
        }
    }
}

$Foo = new Foo;
$Foo->extend(array('name' => 'Bee'));

Now the $Foo object has a public name property with value Bee.

How to change extend function to make variables private ?

Edit Using a private array is another way and definitely not my answer.

回答1:

Just plain, bad design.

What's the purpose of adding a private [!] field at runtime? Existent methods can't rely on such added fields, and you'd be messing with the object functionality.

If you want your object to behave like an hashmap [i.e. you can just call $obj -> newField = $newValue], consider using magic __get and __set methods.

回答2:

You could do something like this.

The __get function will check if the given key is set inside the private property.

class Foo {

private $data = array();

// Accept an array and appends its indexes to the object as property
public function extend($values){
    foreach($values as $i=>$v){
        if(!isset($this->$i))
            $this->data[$i] = $v;
    }
}

public function __get($key) {
    if (isset($this->data[$key])) {
        return $this->data[$key];
    }
}

}

回答3:

I would work with the whole array:

$Foo = new Foo;
$Foo->setOptions(array('name' => 'Bee'));

class Foo {
    private $options = array();

    public function setOptions(array $options) {
        $this->options = $options;
    }

    public function getOption($value = false) {
        if($value) {
            return $this->options[$value];    
        } else {
            return $this->options;
        }
    }
}

Then you have more options when you need other values and you can iterate through the array and work with them. When you have single variable in most cases its a bit complecated.

回答4:

Here is an accessor based approach:

class Extendible
{
    private $properties;

    public function extend(array $properties)
    {
        foreach ($properties as $name => $value) {
            $this->properties[$name] = $value;
        }
    }

    public function __call($method, $parameters)
    {
        $accessor = substr($method, 0, 3);
        $property = lcfirst(substr($method, 3));
        if (($accessor !== 'get' && $accessor !== 'set')
                || !isset($this->properties[$property])) {
            throw new Exception('No such method!');
        }
        switch ($accessor) {
            case 'get':
                return $this->getProperty($property);
                break;
            case 'set':
                return $this->setProperty($property, $parameters[0]);
                break;
        }
    }

    private function getProperty($name)
    {
        return $this->properties[$name];
    }

    private function setProperty($name, $value)
    {
        $this->properties[$name] = $value;
        return $this;
    }
}

Demo:

try {
    $x = new Extendible();
    $x->extend(array('foo' => 'bar'));
    echo $x->getFoo(), PHP_EOL; // Shows 'bar'
    $x->setFoo('baz');
    echo $x->getFoo(), PHP_EOL; // Shows 'baz'
    echo $x->getQuux(), PHP_EOL; // Throws Exception
} catch (Exception $e) {
    echo 'Error: ', $e->getMessage(), PHP_EOL;
}