prevent PHP object from auto-casting

问题

 class Foo 
{
    public $var ;

    function __construct($value) 
    {
         $this->var = $value ;
    }
}
$myFoo = new Foo('hello');
echo $myFoo->var . '<br>' ; // output : hello
// Question : how  can I prevent another programer from accidentaly doing the following
$myFoo = 4 ;
echo $myFoo ; // output : 4

my question is in the comment // Question :...

I would like my coworkers being able to assign values to $myFoo use only $myFoo->var (or whatever public mutators are available in the class Foo)

thank you

EDIT : with all respect to the users who claim it is not possible, SPL_Types PECL extention was able to achieve that (to a certain degree) see e.g http://php.net/manual/en/class.splint.php or http://blog.felixdv.com/2008/01/09/spl_types-in-php-and-strong-typing/

回答1:

You cannot do this in any weakly typed language. If you have functions that take this variable as an argument, you can use type hinting in PHP, but otherwise you cannot prevent people from re-assigning their variables.

This is true to an extent even for strongly typed languages. If a programmer creates two instances of a class, there is no mechanism to prevent them from assigning a different instance to a variable of the same type.

The only way this can happen is if the programmer explicitly uses constants instead of variables (such as using things like final in Java, or val in Scala, etc), but, either way, you have no control over it in any language.

回答2:

You cannot prevent changing the type within the class, but if you make it protected or private and then add a setVariable() method (where Variable is your variable name) you can control the input. Something like:

class myClass {
    protected $integer = 0;
    public function setInteger($new_value)
    {
        if (!is_int($new_value)) {
             throw new RuntimeException('Cannot assign non-integer value to myClass::$integer');
        }
        $this->integer = $new_value;
    }
    public function getInteger()
    {
        return $this->integer;
    }
}

// Now, outside of the class, the $integer property can only be changed using setInteger()
$class = new myClass;
$class->setInteger('dog'); // Uncaught Runtime exception ...
$class->setInteger(5);
echo $class->getInteger(); // 5

An alternative version of that function would accept string numbers and convert them to integers:

    public function setInteger($new_value)
    {
        if (!is_numeric($new_value)) {
             throw new RuntimeException('Cannot assign non-integer value to myClass::$integer');
        }
        $this->integer = (int) $new_value;
    }
$class->setInteger('5'); // 5

来源：https://stackoverflow.com/questions/13905806/prevent-php-object-from-auto-casting

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php

object

casting