see #2: move non-type template param auto to ch02

code/2/2.12.external.template.cpp

@@ -19,5 +19,5 @@ template<bool T> class MagicType {
 int main() {
     // the >> in template
     std::vector<std::vector<int>> matrix;
-    std::vector<MagicType<(1>2)>> magic;
+    std::vector<MagicType<(1>2)>> magic; // legal, but not recommended
 }

code/2/2.14.default.template.param.cpp

@@ -0,0 +1,18 @@
+//
+// 2.4.default.template.param.cpp
+// chapter 2 language usability
+// modern cpp tutorial
+//
+// created by changkun at changkun.de
+//
+
+#include <iostream>
+
+template<typename T = int, typename U = int>
+auto add(T x, U y) -> decltype(x+y) {
+    return x+y;
+}
+
+int main() {
+    std::cout << add(1, 2) << std::endl;
+}

code/2/2.15.variadic.template.param.cpp

@@ -0,0 +1,46 @@
+//
+// 2.15.variadic.template.param.cpp
+// chapter 2 language usability
+// modern cpp tutorial
+//
+// created by changkun at changkun.de
+//
+
+#include <iostream>
+#include <vector>
+#include <string>
+
+// sizeof...
+template<typename... Ts>
+void magic(Ts... args) {
+    std::cout << sizeof...(args) << std::endl;
+}
+
+
+// 1 recursive parameter unpack
+template<typename T0>
+void printf1(T0 value) {
+    std::cout << value << std::endl;
+}
+template<typename T, typename... Ts>
+void printf1(T value, Ts... args) {
+    std::cout << value << std::endl;
+    printf1(args...);
+}
+
+// 2 variadic template parameter unfold
+template<typename T0, typename... T>
+void printf2(T0 t0, T... t) {
+    std::cout << t0 << std::endl;
+    if constexpr (sizeof...(t) > 0) printf2(t...);
+}
+
+int main() {
+    magic();
+    magic(1);
+    magic(1,"");
+    
+    printf1(1, 2, "123", 1.1);
+    printf2(1, 2.3, "abc");
+    return 0;
+}

code/2/2.16.fold.expression.cpp

@@ -1,3 +1,11 @@
+//
+// 2.16.fold.expression.cpp
+// chapter 2 language usability
+// modern cpp tutorial
+//
+// created by changkun at changkun.de
+//
+
 #include <iostream>
 template<typename ... T>
 auto sum(T ... t) {

code/2/2.18.non.type.template.auto.cpp

@@ -0,0 +1,18 @@
+//
+// 2.18.non.type.template.auto.cpp
+// chapter 2 language usability
+// modern cpp tutorial
+//
+// created by changkun at changkun.de
+//
+
+#include <iostream>
+
+template <auto value> void foo() {
+    std::cout << value << std::endl;
+    return;
+}
+
+int main() {
+    foo<10>(); // value is deduced as type int
+}

code/2/todo/2.6.cpp

@@ -1,76 +0,0 @@
-//
-// 2.6.cpp
-// modern c++ tutorial
-//
-// created by changkun at changkun.de
-//
-// 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;
-}

code/2/todo/2.xxx.cpp

@@ -1,21 +0,0 @@
-#include <iostream>
-
-template<typename T0>
-void printf(T0 value) {
-    std::cout << value << std::endl;
-}
-template<typename T, typename... Args>
-void printf(T value, Args... args) {
-    std::cout << value << std::endl;
-    printf(args...);
-}
-
-template<typename T0, typename... T>
-void printf_short(T0 t0, T... t) {
-    std::cout << t0 << std::endl;
-    if constexpr (sizeof...(t) > 0) printf(t...);
-}
-int main() {
-    printf_short(1, 2, "123", 1.1);
-    return 0;
-}