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2/2.6.cpp

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+//
+// 2.6.cpp
+// c++1x tutorial
+//
+// created by changkun at shiyanlou.com
+//
+// 模板增强
+
+
+#include <iostream>
+#include <vector>
+#include <string>
+
+template class std::vector<bool>;            // 强行实例化
+extern template class std::vector<double>;   // 不在该编译文件中实例化模板
+
+
+template< typename T, typename U, int value>
+class SuckType {
+public:
+    T a;
+    U b;
+    SuckType():a(value),b(value){}
+};
+// template< typename T>
+// typedef SuckType<std::vector<int>, T, 1> NewType; // 不合法
+
+template <typename T>
+using NewType = SuckType<int, T, 1>;                 // 合法
+
+// 默认模板类型
+template<typename T = int, typename U = int>
+auto add(T x, U y) -> decltype(x+y) {
+    return x+y;
+}
+
+// sizeof...
+template<typename... Args>
+void magic(Args... args) {
+    std::cout << sizeof...(args) << std::endl;
+}
+
+
+// 1. 递归解参数包
+template<typename T>
+void printf1(T value) {
+    std::cout << value << std::endl;
+}
+template<typename T, typename... Args>
+void printf1(T value, Args... args) {
+    std::cout << value << std::endl;
+    printf1(args...);
+}
+// 2.初始化列表展开解参数包
+template<typename T, typename... Args>
+auto printf2(T value, Args... args) {
+    std::cout << value << std::endl;
+    return std::initializer_list<T>{([&] {
+        std::cout << args << std::endl;
+    }(), value)...};
+}
+
+int main() {
+    
+    std::vector<std::vector<int>> wow;      // 注意尖括号
+    
+    NewType<int> t;
+    
+    magic();
+    magic(1);
+    magic(1,"");
+    
+    printf1(1, 2.3, "abc");
+    printf2(1, 2.3, "abc");
+    return 0;
+}