是什么导致php值是true和false？

Question

I have a class with this function:

public static function getSingleton($modelClass='', array $arguments=array())
{
    $registryKey = '_singleton/'.$modelClass;
    if (!isset(self::$_registry[$registryKey])) {
        if (isset(self::$_registry[$registryKey])) {
            throw new Exception('Mage registry key "'.$registryKey.'" already exists');
        }
        self::$_registry[$registryKey] = self::getModel($modelClass, $arguments);
    }
    return self::$_registry[$registryKey];
}

The exception is being thrown. HOW can the exception be thrown? I can't think of any way that isset() and !isset() could both return true - yet they are! How could this happen? I am using APC, could that have anything to do with it? How would I even debug this?

Answer 1

Isset tests if the variable or index has been initialized or not and does not always use booleans. The value could just as well be null and the proper way of testing this (since PHP is loosely coupled) would be:

if (isset(self::$_registry[$key]) === true)

Or better yet;

if (array_key_exists($key, self::$_registry))

I always suggest using array_key_exists instead of isset since the first one is much more reliable for true/false conditions.

Edit: Also, like the comments stated - your variable is $registryKey and not $key .

Answer 2

It is possible that the object has the magic method __isset() , which may cause some weird behaviours if coded poorly.

Also, it is possible that $registry isn't a simple array but an object which implements the ArrayAccess interface. Then you must look for the __isset() magic method if present, and the method OffsetExists more precisely.