revision #1: 更新第二章中已维护的代码

exercises/2/structured.binding.cpp

@@ -0,0 +1,22 @@
+#include <iostream>
+#include <map>
+#include <string>
+#include <functional>
+
+template <typename Key, typename Value, typename F>
+void update(std::map<Key, Value>& m, F foo) {
+    for (auto&& [key, value] : m ) value = foo(key);
+}
+
+int main() {
+    std::map<std::string, long long int> m {
+        {"a", 1},
+        {"b", 2},
+        {"c", 3}
+    };
+    update(m, [](std::string key) -> long long int {
+        return std::hash<std::string>{}(key);
+    });
+    for (auto&& [key, value] : m)
+        std::cout << key << ":" << value << std::endl;
+}