id,summary,reporter,owner,description,type,status,priority,milestone,component,version,severity,resolution,keywords,cc
20004,Fix NULL and FALSE in WP_Object_Cache and make found/not-found unambiguous.,andy,ryan,"```WP_Object_Cache``` mistreats ```NULL``` as a stored value by converting it to ```""""```. To handle it correctly, the existence check must not use ```isset()```:

{{{
$cache[ $key ] = NULL;
isset( $cache[ $key ] ); // false
array_key_exists( $key, $cache ); // true
}}}

The attached patch corrects the treatment of ```NULL``` by storing it as-is and using ```array_key_exists()``` to test the existence of a key.

As a value returned from ```wp_cache_get```, ```FALSE``` is ambiguous. It could mean that the value stored and retrieved was literally ```FALSE``` or that the key was not found.

The attached patch moves the found/not-found information to a pass-by-reference parameter, ```$found```, which is set to ```TRUE``` after a cache hit or ```FALSE``` after a cache miss. This allows storage and retrieval of ```FALSE``` without ambiguity and reduces the temptation to use confusing patterns such as ```!$value```, ```$value === false```, and ```empty( $value )```.

The attached patch permits a clearer coding style:

{{{
$value = wp_cache_get( $key, $group, false, $found );
if ( ! $found ) {
    $value = $wpdb->get_results( $query );
    wp_cache_set( $key, $value, $group );
}
}}}

However, because object cache drop-ins may lag behind core in adding support for the ```$found``` parameter, the following pattern may be preferred for backwards compatibility:

{{{
$value = wp_cache_get( $key, $group, false, $found );
if ( ! $value && ! $found ) {
    $value = $wpdb->get_results( $query );
    wp_cache_set( $key, $value, $group );
}
}}}

I also added a function, ```wp_cache_found()```, to determine whether the previous retrieval was a hit or a miss.

{{{
$value = wp_cache_get( $key, $group );
if ( ! wp_cache_found() ) {
    $value = $wpdb->get_results( $query );
    wp_cache_set( $key, $value, $group );
}
}}}

Again, this function may not be present in drop-ins. Until such time as old drop-ins are forced into obsolescence, use ```function_exists``` before calling ```wp_cache_found``` in core code.

It would behoove us to devise a drop-in API versioning and update system to assist with this.",defect (bug),closed,normal,3.4,Cache,,normal,fixed,has-patch dev-feedback,