book: translate ch03

see #12

code/3/3.7.perfect.forward.cpp

@@ -0,0 +1,37 @@
+//
+// 3.6.perfect.forward.cpp
+// modern c++ tutorial
+//
+// created by changkun at changkun.de
+// https://github.com/changkun/modern-cpp-tutorial
+//
+
+#include <iostream>
+#include <utility>
+void reference(int& v) {
+    std::cout << "lvalue reference" << std::endl;
+}
+void reference(int&& v) {
+    std::cout << "rvalue reference" << std::endl;
+}
+template <typename T>
+void pass(T&& v) {
+    std::cout << "          normal param passing: ";
+    reference(v);
+    std::cout << "       std::move param passing: ";
+    reference(std::move(v));
+    std::cout << "    std::forward param passing: ";
+    reference(std::forward<T>(v));
+    std::cout << "static_cast<T&&> param passing: ";
+    reference(static_cast<T&&>(v));
+}
+int main() {
+    std::cout << "rvalue pass:" << std::endl;
+    pass(1);
+    
+    std::cout << "lvalue pass:" << std::endl;
+    int l = 1;
+    pass(l);
+    
+    return 0;
+}