src/Container.php
public function has($id): bool
    {
        return isset($this->entries[$id]) || isset($this->entryCache[$id]);
    }
public function has($id): bool
    {
        return isset($this->entries[$id]) || isset($this->entryCache[$id]);
    }
Tells if the entry with the given identifier exists in the container.
@param string $id The entry identifier to look for
@return bool True if an entry with the given identifier exists, false otherwise