子類

class API
{
public:
    static API& instance();
    
    virtual ~API() {}
    
    virtual const char* func1() = 0;
    virtual void func2() = 0;
    
protected:
    API() {}
    API(const API&) = delete;
    API& operator=(const API&) = delete;
};

class WindowsAPI : public API
{
public:
    virtual const char* func1()  override { /* Windows code */ }
    virtual void func2() override { /* Windows code */ }    
};

class LinuxAPI : public API
{
public:
    virtual const char* func1() override { /* Linux code */ }
    virtual void func2() override { /* Linux code */ }    
};

API& API::instance() {
#if PLATFORM == WIN32
    static WindowsAPI instance;
#elif PLATFORM = LINUX
    static LinuxAPI instance;
#endif
    return instance;
}

在此示例中，簡單的編譯器開關將 API 類繫結到適當的子類。通過這種方式，可以訪問 API 而無需耦合到特定於平臺的程式碼。