revision #1: 更新第二章中已维护的代码

code/2/2.10.if.constexpr.cpp

@@ -0,0 +1,31 @@
+//
+// 2.10.if.constexpr.cpp
+// chapter 2 language usability
+// modern cpp tutorial
+//
+// created by changkun at changkun.de
+//
+
+#include <iostream>
+
+template<typename T>
+auto print_type_info(const T& t) {
+    if constexpr (std::is_integral<T>::value) {
+        return t + 1;
+    } else {
+        return t + 0.001;
+    }
+}
+
+// at compiling time
+// int print_type_info(const int& t) {
+//     return t + 1;
+// }
+// double print_type_info(const double& t) {
+//     return t + 0.001;
+// }
+
+int main() {
+    std::cout << print_type_info(5) << std::endl;
+    std::cout << print_type_info(3.14) << std::endl;
+}