__isset() Method

__isset() is a magic method: it is called when the existence of a property has to be checked.

That way, it is possible to create dynamically properties, without hardcoding them.

The __isset() method is usually paired with the __get() and __set() methods.

<?php

class x {
    private $values = ['a' => 1,
                       'b' => 2,
                       ];

    function __isset($name) {
        return isset($this->values[$name]);
    }
}

?>

Documentation

See also A Look At PHP’s isset().

Related : Magic Methods, __set() Method, __get() Method, __unset() Method, Isset, Magic Property