One way of thinking about access specifiers in C++/WinRT implementation types

# One way of thinking about access specifiers in C++/WinRT implementation types - The Old New Thing Source: [https://devblogs.microsoft.com/oldnewthing/20261009-00/?p=112764/](https://devblogs.microsoft.com/oldnewthing/20261009-00/?p=112764/) In C\+\+/WinRT, Windows Runtime classes are exposed to the outside world through the projection, but internally they are represented by their implementation type\. Since the outside world sees only the projection, implementation types are visible only to the module that produced them\. This realization lets you reinterpret the C\+\+ access specifiers for C\+\+/WinRT implementation types\. Declared on implementation asC\# and C\+\+/CX equivalentAccessible toimplemented interfacepublicAnyonepublicinternalCode in the same moduleprotectedprotectedCode in derived classesprivateprivateCode in the same classIn code: ``` struct Widget : winrt::implements<Widget, IStringable> { public: // This is a member of IStringable, // so it is accessible to anyone. winrt::hstring ToString(); // This does not implement any member from IStringable, // so it is accessible to other code in the same module. void Recolor(winrt::Windows::UI::Color newColor); protected: // Accessible to implementation classes that derive from Widget. void Reverse(); private: // Accessible only to Widget itself. void Reset(); }; ``` Note that if you are implementing a runtime class, then C\+\+/WinRT autogenerates a template for you that auto\-declares all of the declared interfaces of that class\. ``` // Widget.idl namespace Contoso { runtimeclass Widget : Windows.Foundation.IStringable { String Name{ get; }; void Toggle(); } } ``` The IDL compiler autogenerates an interface`IWidget`with a property`Name`and a method`Toggle\(\)`\. ``` // implementation namespace winrt::Contoso { struct Widget : WidgetT<Widget> { ⟦ ... ⟧ }; } ``` The`WidgetT<Widget\>`expands to`implements<Widget, IWidget, Windows::Foundation::IStringable\>`because those are the interfaces declared by the IDL file\. ### Category ### Topics ## Author  Raymond has been involved in the evolution of Windows for more than 30 years\. In 2003, he began a Web site known as The Old New Thing which has grown in popularity far beyond his wildest imagination, a development which still gives him the heebie\-jeebies\. The Web site spawned a book, coincidentally also titled The Old New Thing \(Addison Wesley 2007\)\. He occasionally appears on the Windows Dev Docs Twitter account to tell stories which convey no useful information\.