Recursive lambda fn in CPP

For an annonymous lambda function in Cpp, when you want to self reference it using the following way, always put the return type in the signature.

    vvi e(n + 1); // edge list

    vi parent(n + 1, 0);
    vi depth(n + 1, 0);

    // always put return type when doing self referencing
    auto dfs = [&](auto self, int root, int d) -> void {
        depth[root] = d;
        for (int x : e[root]) {
            if (x != parent[root]) {
                parent[x] = root;
                self(self, x, d + 1);
            }
        }
    };

    dfs(dfs, 1, 1);