private function allowedCallbacks(array $callbacks, $which)
    {
        $reserved = $this->locked ? array_flip(array_keys($this->$which)) : [];

        return array_diff_key(array_filter($callbacks, 'is_callable'), $reserved);
    }
private function allowedCallbacks(array $callbacks, $which)
    {
        $reserved = $this->locked ? array_flip(array_keys($this->$which)) : [];

        return array_diff_key(array_filter($callbacks, 'is_callable'), $reserved);
    }
private function allowedCallbacks ( array $ callbacks , $ which ) { $ reserved = $ this -> locked ? array_flip ( array_keys ( $ this -> $ which ) ) : [ ] ; return array_diff_key ( array_filter ( $ callbacks , 'is_callable' ) , $ reserved ) ; }
Ensure items in callback array are actually callbacks and their names are not used by Foil

@param  array  $callbacks
@param  string $which     "functions" or "filters"
@return array
@access private
Ensure items in callback array are actually callbacks and their names are not used by Foil