diff --git a/.gitignore b/.gitignore
index 98629db..7aabc6b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 i
 s
 t
+.clangd
diff --git a/track.cpp b/track.cpp
index 3af2fa3..a2c39de 100644
--- a/track.cpp
+++ b/track.cpp
@@ -1,5 +1,6 @@
 #include <iostream>
 #include <ostream>
+// requires C++23 to compile
 class A {
   long long counter = 0;
 
@@ -10,7 +11,8 @@ public:
     ret.counter++;
     return ret;
   }
-  A operator[](int dummy) {
+  // requires C++23 to compile
+  A operator[](int _ = 0) {
     A ret = *this;
     ret.counter--;
     return ret;
@@ -23,8 +25,8 @@ public:
 
 int main(void) {
   A a;
-  std::cout << a[0] << std::endl;
-  std::cout << a[0]() << std::endl;
-  std::cout << a[0]()() << std::endl;
+  std::cout << a[] << std::endl;
+  std::cout << a[]() << std::endl;
+  std::cout << a[]()() << std::endl;
   return 0;
 }