book: translate ch02

Update #12

code/2/2.19.delegate.constructor.cpp

@@ -0,0 +1,66 @@
+//
+// 2.19.constructor.cpp
+// chapter 2 language usability
+// modern c++ tutorial
+//
+// created by changkun at changkun.de
+// https://github.com/changkun/modern-cpp-tutorial
+//
+
+#include <iostream>
+#include <string>
+class Base {
+public:
+    std::string str;
+    int value;
+    Base() = delete;
+    Base(std::string s) {
+        str = s;
+    }
+    
+    // delegate constructor
+    Base(std::string s, int v) : Base(s) {
+        value = v;
+    }
+    
+    // final constructor
+    virtual void foo() final {
+        return;
+    }
+    virtual void foo(int v) {
+        value = v;
+    }
+};
+class Subclass final : public Base {
+public:
+    double floating;
+    Subclass() = delete;
+    
+    // inherit constructor
+    Subclass(double f, int v, std::string s) : Base(s, v) {
+        floating = f;
+    }
+    
+    // explifict constructor
+    virtual void foo(int v) override {
+        std::cout << v << std::endl;
+        value = v;
+    }
+};  // legal final
+
+// class Subclass2 : Subclass {
+// };  // illegal, Subclass has final
+// class Subclass3 : Base {
+//    void foo(); // illegal, foo has final
+// }
+
+int main() {
+    // Subclass oops; // illegal, default constructor has deleted
+    Subclass s(1.2, 3, "abc");
+    
+    s.foo(1);
+    
+    std::cout << s.floating << std::endl;
+    std::cout << s.value << std::endl;
+    std::cout << s.str << std::endl;
+}