policy-based design

呵呵，有点类似策略模式，不过是用模板实现的。

template< typename output_policy, typename language_policy>class HelloWorld : public output_policy, public language_policy{ using output_policy::Print; using language_policy::Message;public: //behaviour method void Run() { //two policy methods Print( Message() ); }}; #include <iostream> class HelloWorld_OutputPolicy_WriteToCout{ protected: template< typename message_type > void Print( message_type message ) { std::cout << message << std::endl; }}; #include <string> class HelloWorld_LanguagePolicy_English{ protected: std::string Message() { return "Hello, World!"; }}; class HelloWorld_LanguagePolicy_German{ protected: std::string Message() { return "Hallo Welt!"; }}; int main(){ /* example 1 */ typedef HelloWorld < HelloWorld_OutputPolicy_WriteToCout, HelloWorld_LanguagePolicy_English > my_hello_world_type; my_hello_world_type hello_world; hello_world.Run(); // Prints "Hello, World!" /* example 2 * does the same but uses another policy, the language has changed */ typedef HelloWorld< HelloWorld_OutputPolicy_WriteToCout, HelloWorld_LanguagePolicy_German > my_other_hello_world_type; my_other_hello_world_type hello_world2; hello_world2.Run(); // Prints "Hallo Welt!"}