prepare for c++17

code/2/2.3.cpp

@@ -0,0 +1,49 @@
+//
+// 2.3.cpp
+// c++1x tutorial
+//
+// created by changkun at shiyanlou.com
+//
+// auto/decltype/尾返回类型/返回类型推导
+
+
+#include <iostream>
+
+// 传统 C++
+template <typename R, typename T, typename U>
+R add1(T x, U y) {
+    return x+y;
+}
+
+// 尾返回类型
+template <typename T, typename U>
+auto add2(T x, U y) -> decltype(x+y) {
+    return x+y;
+}
+
+// C++14 返回类型推导
+template <typename T, typename U>
+auto add3(T x, U y) {
+    return x+y;
+}
+
+int main() {
+    auto i = 5;
+    
+    int arr[10] = {0};
+    auto auto_arr = arr;        // 正确，对整个类型进行推导
+    //auto auto_arr2[10] = arr; // 错误,  无法推导数组元素类型
+
+    auto x = 1;
+    auto y = 2;
+    decltype(x+y) z1;
+    //auto z2;                  // 错误, 无法推导
+
+    
+    std::cout << add1<int, int, int>(1,1) << std::endl;
+    std::cout << add1<int, int>(1,1) << std::endl;
+    std::cout << add1<int, int>(1,1) << std::endl;
+    
+    
+    return 0;
+}