library: c++23 deducing this for all 22 recursive lambdas; tester.sh to c++23

Cameron Custer · Cameron Custer · commit 2aa21185b3dc · 2026-07-06T22:30:55.000-07:00
diff --git a/library/contest/tester.sh b/library/contest/tester.sh
@@ -1,9 +1,9 @@
 # https://github.com/Errichto/youtube/blob/master/testing/s.sh
 # bash tester.sh a naive gen
 
-g++ -std=c++20 -g -D_GLIBCXX_DEBUG -fsanitize=address,undefined $1.cpp -o $1.out
-g++ -std=c++20 $2.cpp -o $2.out
-g++ -std=c++20 $3.cpp -o $3.out
+g++ -std=c++23 -g -D_GLIBCXX_DEBUG -fsanitize=address,undefined $1.cpp -o $1.out
+g++ -std=c++23 $2.cpp -o $2.out
+g++ -std=c++23 $3.cpp -o $3.out
 
 for((i = 1; ; ++i))
 do
diff --git a/library/convolution/min_plus_convolution_convex_and_arbitrary.hpp b/library/convolution/min_plus_convolution_convex_and_arbitrary.hpp
@@ -9,7 +9,7 @@ vi min_plus(const vi& convex, const vi& arbitrary) {
   int n = sz(convex);
   int m = sz(arbitrary);
   vi res(n + m - 1, INT_MAX);
-  auto dnc = [&](auto&& dnc, int res_le, int res_ri,
+  auto dnc = [&](this auto&& dnc, int res_le, int res_ri,
                int arb_le, int arb_ri) {
     if (res_le >= res_ri) return;
     int mid_res = (res_le + res_ri) / 2;
@@ -22,10 +22,9 @@ vi min_plus(const vi& convex, const vi& arbitrary) {
         op_arb = i;
       }
     }
-    dnc(dnc, res_le, mid_res, arb_le,
-      min(arb_ri, op_arb + 1));
-    dnc(dnc, mid_res + 1, res_ri, op_arb, arb_ri);
+    dnc(res_le, mid_res, arb_le, min(arb_ri, op_arb + 1));
+    dnc(mid_res + 1, res_ri, op_arb, arb_ri);
   };
-  dnc(dnc, 0, n + m - 1, 0, m);
+  dnc(0, n + m - 1, 0, m);
   return res;
 }
diff --git a/library/graphs/bcc_callback.hpp b/library/graphs/bcc_callback.hpp
@@ -44,11 +44,11 @@
 void bcc(const auto& g, auto f) {
   int n = sz(g), q = 0, s = 0;
   vi t(n), st(n);
-  auto dfs = [&](auto&& dfs, int u) -> int {
+  auto dfs = [&](this auto&& dfs, int u) -> int {
     int l = t[u] = ++q;
     for (int v : g[u]) {
       int siz = s, lu = 0;
-      l = min(l, t[v] ?: (lu = dfs(dfs, st[s++] = v)));
+      l = min(l, t[v] ?: (lu = dfs(st[s++] = v)));
       if (lu >= t[u]) {
         st[s++] = u;
         f({siz + all(st) - n + s});
@@ -57,5 +57,5 @@ void bcc(const auto& g, auto f) {
     }
     return l;
   };
-  rep(i, 0, n) if (!t[i]) dfs(dfs, i);
+  rep(i, 0, n) if (!t[i]) dfs(i);
 }
diff --git a/library/graphs/euler_path.hpp b/library/graphs/euler_path.hpp
@@ -16,15 +16,15 @@
 vector<pii> euler_path(auto& g, int m, int s) {
   vi vis(m);
   vector<pii> path;
-  auto dfs = [&](auto&& dfs, int u, int eu) -> void {
+  auto dfs = [&](this auto&& dfs, int u, int eu) -> void {
     while (!empty(g[u])) {
       auto [v, ev] = g[u].back();
       g[u].pop_back();
-      if (!vis[ev]) vis[ev] = 1, dfs(dfs, v, ev);
+      if (!vis[ev]) vis[ev] = 1, dfs(v, ev);
     }
     path.emplace_back(u, eu);
   };
-  dfs(dfs, s, -1);
+  dfs(s, -1);
   ranges::reverse(path);
   return path;
 }
diff --git a/library/graphs/scc.hpp b/library/graphs/scc.hpp
@@ -11,18 +11,17 @@
 auto scc(const auto& g) {
   int n = sz(g), num_sccs = 0, q = 0, s = 0;
   vi scc_id(n, -1), tin(n), st(n);
-  auto dfs = [&](auto&& dfs, int u) -> int {
+  auto dfs = [&](this auto&& dfs, int u) -> int {
     int low = tin[u] = ++q;
     st[s++] = u;
     for (int v : g[u])
-      if (scc_id[v] < 0)
-        low = min(low, tin[v] ?: dfs(dfs, v));
+      if (scc_id[v] < 0) low = min(low, tin[v] ?: dfs(v));
     if (tin[u] == low) {
       while (scc_id[u] < 0) scc_id[st[--s]] = num_sccs;
       num_sccs++;
     }
     return low;
   };
-  rep(i, 0, n) if (!tin[i]) dfs(dfs, i);
+  rep(i, 0, n) if (!tin[i]) dfs(i);
   return pair{num_sccs, scc_id};
 }
diff --git a/library/graphs/strongly_connected_components/add_edges_strongly_connected.hpp b/library/graphs/strongly_connected_components/add_edges_strongly_connected.hpp
@@ -29,12 +29,12 @@ vector<pii> extra_edges(const auto& g, int num_sccs,
     zero_in[scc_id[v]] = 0;
   }
   vector<bool> vis(num_sccs);
-  auto dfs = [&](auto&& dfs, int u) {
+  auto dfs = [&](this auto&& dfs, int u) {
     if (empty(scc_g[u])) return u;
     for (int v : scc_g[u])
       if (!vis[v]) {
         vis[v] = 1;
-        int zero_out = dfs(dfs, v);
+        int zero_out = dfs(v);
         if (zero_out != -1) return zero_out;
       }
     return -1;
@@ -43,7 +43,7 @@ vector<pii> extra_edges(const auto& g, int num_sccs,
   vi in_unused;
   rep(i, 0, num_sccs) if (zero_in[i]) {
     vis[i] = 1;
-    int zero_out = dfs(dfs, i);
+    int zero_out = dfs(i);
     if (zero_out != -1) edges.emplace_back(zero_out, i);
     else in_unused.push_back(i);
   }
diff --git a/library/graphs/strongly_connected_components/offline_incremental_scc.hpp b/library/graphs/strongly_connected_components/offline_incremental_scc.hpp
@@ -16,7 +16,7 @@ vi offline_incremental_scc(vector<array<int, 2>> eds,
   vi ids(n, -1), joins(m, m), idx(m), vs(n), scc_id;
   iota(all(idx), 0);
   vector<vi> g;
-  auto dnc = [&](auto&& dnc, auto el, auto er, int tl,
+  auto dnc = [&](this auto&& dnc, auto el, auto er, int tl,
                int tr) {
     g.clear();
     int mid = midpoint(tl, tr);
@@ -42,11 +42,11 @@ vi offline_incremental_scc(vector<array<int, 2>> eds,
       auto& [u, v] = eds[*it];
       u = scc_id[u], v = scc_id[v];
     }
-    dnc(dnc, el, split, tl, mid);
-    dnc(dnc, split, er, mid, tr);
+    dnc(el, split, tl, mid);
+    dnc(split, er, mid, tr);
   };
   // uses -1 as the lower bound to correctly handle
   // self-edges
-  dnc(dnc, all(idx), -1, m);
+  dnc(all(idx), -1, m);
   return joins;
 }
diff --git a/library/graphs/uncommon/bridges.hpp b/library/graphs/uncommon/bridges.hpp
@@ -18,19 +18,19 @@
 auto bridges(const auto& g, int m) {
   int n = sz(g), num_ccs = 0, q = 0, s = 0;
   vi br_id(n, -1), is_br(m), tin(n), st(n);
-  auto dfs = [&](auto&& dfs, int u, int p) -> int {
+  auto dfs = [&](this auto&& dfs, int u, int p) -> int {
     int low = tin[u] = ++q;
     st[s++] = u;
     for (auto [v, e] : g[u])
       if (e != p && br_id[v] < 0)
-        low = min(low, tin[v] ?: dfs(dfs, v, e));
+        low = min(low, tin[v] ?: dfs(v, e));
     if (tin[u] == low) {
       if (p != -1) is_br[p] = 1;
       while (br_id[u] < 0) br_id[st[--s]] = num_ccs;
       num_ccs++;
     }
     return low;
   };
-  rep(i, 0, n) if (!tin[i]) dfs(dfs, i, -1);
+  rep(i, 0, n) if (!tin[i]) dfs(i, -1);
   return tuple{num_ccs, br_id, is_br};
 }
diff --git a/library/graphs/uncommon/cuts.hpp b/library/graphs/uncommon/cuts.hpp
@@ -19,14 +19,14 @@
 auto cuts(const auto& g, int m) {
   int n = sz(g), num_bccs = 0, q = 0, s = 0;
   vi bcc_id(m, -1), is_cut(n), tin(n), st(m);
-  auto dfs = [&](auto&& dfs, int u, int p) -> int {
+  auto dfs = [&](this auto&& dfs, int u, int p) -> int {
     int low = tin[u] = ++q;
     for (auto [v, e] : g[u]) {
       assert(u != v);
       if (e == p) continue;
       if (tin[v] < tin[u]) st[s++] = e;
       int lu = -1;
-      low = min(low, tin[v] ?: (lu = dfs(dfs, v, e)));
+      low = min(low, tin[v] ?: (lu = dfs(v, e)));
       if (lu >= tin[u]) {
         is_cut[u] = p >= 0 || tin[u] + 1 < tin[v];
         while (bcc_id[e] < 0) bcc_id[st[--s]] = num_bccs;
@@ -35,6 +35,6 @@ auto cuts(const auto& g, int m) {
     }
     return low;
   };
-  rep(i, 0, n) if (!tin[i]) dfs(dfs, i, -1);
+  rep(i, 0, n) if (!tin[i]) dfs(i, -1);
   return tuple{num_bccs, bcc_id, is_cut};
 }
diff --git a/library/trees/centroid_decomp.hpp b/library/trees/centroid_decomp.hpp
@@ -8,19 +8,20 @@
 //! @space O(n)
 vi cd(auto& g, auto f) {
   vi p(sz(g), -1), s(sz(g), sz(g));
-  auto ctd = [&](auto&& ctd, int u, int p, int n) -> int {
+  auto ctd = [&](this auto&& ctd, int u, int p,
+               int n) -> int {
     s[u] = 1;
     for (int v : g[u])
       if (v != p) {
-        if (int c = ctd(ctd, v, u, n); c != -1) return c;
+        if (int c = ctd(v, u, n); c != -1) return c;
         s[u] += s[v];
       }
     return 2 * s[u] >= n ? s[p] = n - s[u], u : -1;
   };
-  auto dfs = [&](auto&& dfs, int u) -> int {
-    f(u = ctd(ctd, u, u, s[u]));
-    for (int v : g[u]) erase(g[v], u), p[dfs(dfs, v)] = u;
+  auto dfs = [&](this auto&& dfs, int u) -> int {
+    f(u = ctd(u, u, s[u]));
+    for (int v : g[u]) erase(g[v], u), p[dfs(v)] = u;
     return u;
   };
-  return dfs(dfs, 0), p;
+  return dfs(0), p;
 }
diff --git a/library/trees/edge_cd.hpp b/library/trees/edge_cd.hpp
@@ -15,18 +15,19 @@
 //! @space O(n)
 template<class G> void edge_cd(vector<G>& g, auto f) {
   vi s(sz(g));
-  auto ctd = [&](auto&& ctd, int u, int p, int m) -> int {
+  auto ctd = [&](this auto&& ctd, int u, int p,
+               int m) -> int {
     s[u] = 1;
     for (int v : g[u])
       if (v != p) {
-        if (int c = ctd(ctd, v, u, m); c != -1) return c;
+        if (int c = ctd(v, u, m); c != -1) return c;
         s[u] += s[v];
       }
     return 2 * s[u] > m ? s[p] = m + 1 - s[u], u : -1;
   };
-  auto dfs = [&](auto&& dfs, int u, int m) {
+  auto dfs = [&](this auto&& dfs, int u, int m) {
     if (m < 2) return;
-    u = ctd(ctd, u, u, m);
+    u = ctd(u, u, m);
     int sum = 0;
     auto it = partition(all(g[u]), [&](int v) {
       ll x = sum + s[v];
@@ -35,9 +36,9 @@ template<class G> void edge_cd(vector<G>& g, auto f) {
     f(u, it - begin(g[u]));
     G oth(it, end(g[u]));
     g[u].erase(it, end(g[u]));
-    dfs(dfs, u, sum);
+    dfs(u, sum);
     swap(g[u], oth);
-    dfs(dfs, u, m - sum);
+    dfs(u, m - sum);
   };
-  dfs(dfs, 0, sz(g) - 1);
+  dfs(0, sz(g) - 1);
 };
diff --git a/library/trees/hld.hpp b/library/trees/hld.hpp
@@ -14,24 +14,24 @@ template<bool VALS_EDGES> struct HLD {
   int n;
   vi p, siz, rt, tin;
   HLD(auto& g): n(sz(g)), p(n), siz(n, 1), rt(n), tin(n) {
-    auto dfs1 = [&](auto dfs1, int u) -> void {
+    auto dfs1 = [&](this auto&& dfs1, int u) -> void {
       for (int& v : g[u]) {
         erase(g[v], p[v] = u);
-        dfs1(dfs1, v);
+        dfs1(v);
         siz[u] += siz[v];
         if (siz[v] > siz[g[u][0]]) swap(v, g[u][0]);
       }
     };
-    dfs1(dfs1, 0);
+    dfs1(0);
     int tim = 0;
-    auto dfs2 = [&](auto dfs2, int u) -> void {
+    auto dfs2 = [&](this auto&& dfs2, int u) -> void {
       tin[u] = tim++;
       for (int v : g[u]) {
         rt[v] = (v == g[u][0] ? rt[u] : v);
-        dfs2(dfs2, v);
+        dfs2(v);
       }
     };
-    dfs2(dfs2, 0);
+    dfs2(0);
   }
   void path(int u, int v, auto f) {
     for (;; v = p[rt[v]]) {
diff --git a/library/trees/lca_rmq.hpp b/library/trees/lca_rmq.hpp
@@ -16,14 +16,13 @@ struct LCA {
   LCA(const auto& g):
     n(sz(g)), tin(n), siz(n, 1), d(n), p(n) {
     vi order;
-    auto dfs = [&](auto&& dfs, int u) -> void {
+    auto dfs = [&](this auto&& dfs, int u) -> void {
       tin[u] = sz(order), order.push_back(u);
       for (int v : g[u])
         if (v != p[u])
-          d[v] = d[p[v] = u] + 1, dfs(dfs, v),
-          siz[u] += siz[v];
+          d[v] = d[p[v] = u] + 1, dfs(v), siz[u] += siz[v];
     };
-    dfs(dfs, 0);
+    dfs(0);
     rmq = {order,
       [&](int u, int v) { return d[u] < d[v] ? u : v; }};
   }
diff --git a/library/trees/linear_lca.hpp b/library/trees/linear_lca.hpp
@@ -13,17 +13,17 @@ struct linear_lca {
   linear_lca(const auto& g):
     n(sz(g)), d(n), in(n), asc(n), head(n + 1) {
     vector<pii> order;
-    auto dfs = [&](auto&& dfs, int u, int p) -> void {
+    auto dfs = [&](this auto&& dfs, int u, int p) -> void {
       order.emplace_back(u, p), in[u] = sz(order);
       for (int v : g[u])
         if (v != p) {
           d[v] = 1 + d[u];
-          dfs(dfs, v, u);
+          dfs(v, u);
           head[in[v]] = u;
           if (lsb(in[u]) < lsb(in[v])) in[u] = in[v];
         }
     };
-    dfs(dfs, 0, 0);
+    dfs(0, 0);
     for (auto [u, p] : order) asc[u] = asc[p] | lsb(in[u]);
   }
   int lca(int u, int v) {
diff --git a/library/trees/shallowest_decomp_tree.hpp b/library/trees/shallowest_decomp_tree.hpp
@@ -9,18 +9,18 @@
 //! @space O(n)
 void shallowest(auto& g, auto f) {
   vector<vi> order(bit_width(size(g)));
-  auto dfs = [&](auto&& dfs, int u, int p) -> int {
+  auto dfs = [&](this auto&& dfs, int u, int p) -> int {
     int once = 0, twice = 0;
     for (int v : g[u])
       if (v != p) {
-        int dp = dfs(dfs, v, u);
+        int dp = dfs(v, u);
         twice |= once & dp, once |= dp;
       }
     auto dp = (once | (bit_ceil(twice + 1u) - 1)) + 1;
     order[countr_zero(dp)].push_back(u);
     return dp;
   };
-  dfs(dfs, 0, 0);
+  dfs(0, 0);
   for (const vi& vec : order | views::reverse)
     for (int u : vec) {
       f(u);
diff --git a/library/trees/tree_lift.hpp b/library/trees/tree_lift.hpp
@@ -11,14 +11,14 @@
 struct tree_lift {
   vi d, p, j;
   tree_lift(const auto& g): d(sz(g)), p(d), j(d) {
-    auto dfs = [&](auto&& dfs, int u) -> void {
+    auto dfs = [&](this auto&& dfs, int u) -> void {
       int up = d[u] + d[j[j[u]]] == 2 * d[j[u]] ? j[j[u]]
                                                 : u;
       for (int v : g[u])
         if (v != p[u])
-          d[v] = d[p[v] = u] + 1, j[v] = up, dfs(dfs, v);
+          d[v] = d[p[v] = u] + 1, j[v] = up, dfs(v);
     };
-    dfs(dfs, 0);
+    dfs(0);
   }
   int kth_par(int u, int k) {
     int anc_d = d[u] - k;
diff --git a/library/trees/uncommon/hagerup_kth_par.hpp b/library/trees/uncommon/hagerup_kth_par.hpp
@@ -21,22 +21,22 @@ template<int K = 2> struct hagerup {
       jmp[t] = st[max(0, s - K * (t & -t))];
       t++;
     };
-    auto dfs = [&](auto&& dfs, int u, int p) -> void {
+    auto dfs = [&](this auto&& dfs, int u, int p) -> void {
       int& l = leaf[u] = st[d[u]] = u;
       pos[u] = t;
       calc(d[u]);
       for (int v : g[u])
         if (v != p) {
           d[v] = 1 + d[u];
-          dfs(dfs, v, u);
+          dfs(v, u);
           if (d[l] < d[leaf[v]]) l = leaf[v];
           calc(d[u]);
         }
       int s = (d[l] - d[u]) * (2 * K + 3) / K;
       s = min(max(s, 2 * K), d[l] + 1);
       rep(i, sz(lad[l]), s) lad[l].push_back(st[d[l] - i]);
     };
-    dfs(dfs, 0, 0);
+    dfs(0, 0);
   }
   int kth_par(int u, int k) {
     assert(0 <= k && k <= d[u]);
diff --git a/library/trees/uncommon/ladder_decomposition.hpp b/library/trees/uncommon/ladder_decomposition.hpp
diff --git a/library/trees/uncommon/linear_kth_par.hpp b/library/trees/uncommon/linear_kth_par.hpp
diff --git a/library/trees/uncommon/subtree_isomorphism.hpp b/library/trees/uncommon/subtree_isomorphism.hpp
