foo.cc: In function ‘void tree::insert(int, const char*, int)’:
foo.cc:307:10: warning: structured bindings only available with ‘-std=c++17’ or ‘-std=gnu++17’ [-Wc++17-extensions]
  307 |     auto [l, l_sz, r] = split(root, total_size, index);
      |          ^
foo.cc: In function ‘void tree::erase(int, int)’:
foo.cc:340:10: warning: structured bindings only available with ‘-std=c++17’ or ‘-std=gnu++17’ [-Wc++17-extensions]
  340 |     auto [l, l_sz, rest] = split(root, total_size, index);
      |          ^
foo.cc:341:10: warning: structured bindings only available with ‘-std=c++17’ or ‘-std=gnu++17’ [-Wc++17-extensions]
  341 |     auto [mid, mid_sz, r] = split(rest, total_size - l_sz, len);
      |          ^