src/Container/Container.php
public function has($id)
    {
        return isset($this->instances[$id]) || $this->extra->has($id);
    }
public function has($id)
    {
        return isset($this->instances[$id]) || $this->extra->has($id);
    }
Returns true if the container can return an entry for the given identifier.

@param  string $id
@return boolean