struct Node {
    ll l, r;
    mutable ll v;

    Node(ll l, ll r = 0, ll v = 0) : l(l), r(r), v(v) {}

    bool operator<(const Node &a) const {
        return l < a.l;
    }
};

想问下这段代码里面中间那句

    Node(ll l, ll r = 0, ll v = 0) : l(l), r(r), v(v) {}

是什么意思