{"ast_node_type":"function","tokens":[{"end":76,"kind":"keyword","start":0,"text":"fn"}]}
    fn index_mut(&mut self, _key: Key<P::K, P::V, P>) -> &mut Self::Output {
impl<P: Policy> IndexMut<Key<P::K, P::V, P>> for DynMap {
        // Safe due to `#[repr(transparent)]`.