implemented track fully just need to do test code for it

.gitignore

@@ -1,3 +1,3 @@
 i
 s
-
+t

track.cpp

@@ -0,0 +1,30 @@
+#include <iostream>
+#include <ostream>
+class A {
+  long long counter = 0;
+
+public:
+  A() : counter{0} {}
+  A operator()() {
+    A ret = *this;
+    ret.counter++;
+    return ret;
+  }
+  A operator[](int dummy) {
+    A ret = *this;
+    ret.counter--;
+    return ret;
+  }
+  friend std::ostream &operator<<(std::ostream &lhs, A const &rhs) {
+    lhs << rhs.counter;
+    return lhs;
+  }
+};
+
+int main(void) {
+  A a;
+  std::cout << a[0] << std::endl;
+  std::cout << a[0]() << std::endl;
+  std::cout << a[0]()() << std::endl;
+  return 0;
+}