用常量实例化不同对象时的PHP注意事项

Question

I understand you cannot duplicate constant. I am just confused as to why it does not work with different objects.

In one of my project I used them to pass settings to my object.

Here is an example:

class someClass {

    function __construct($config) {
        define("PRIVATE_KEY", $config['private_key']);
    }
}

and here is how I create the objects

$objectA = new someClass($config['A']);
$objectB = new someClass($config['B']); //ERROR!!

I get the error:

Constant PRIVATE_KEY already defined

Most people that get this error had included the same constant multiple times.

In My case they are being used in separate objects. I will add some check to make sure they are not being redefined. but I am still curious to know why this happening.

Aren't object disposed/destroyed when no longer used?

Answer 1

Yes, objects are destroyed at some point, but define declarations are global and persist until they are undefined. Your code is defining the same constant twice.

Private properties, static properties, or maybe class constants are more appropriate for what you're attempting to do since they are encapsulated within the object.

class someClass {

    private $private_key;

    // constructor
    function __construct($config) {
        $this->private_key = $config['private_key'];
    }
}