{"id":112803,"date":"2026-10-28T07:00:00","date_gmt":"2026-10-28T14:00:00","guid":{"rendered":"https:\/\/devblogs.microsoft.com\/oldnewthing\/?p=112803"},"modified":"2026-10-28T12:55:36","modified_gmt":"2026-10-28T19:55:36","slug":"20261028-00","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20261028-00\/?p=112803\/","title":{"rendered":"C++\/WinRT overcorrection: Using make_self<\/CODE> and immediately converting it to the projected interface"},"content":{"rendered":"

In C++\/WinRT, there are two ways of creating objects that you yourself implement.<\/p>\n

For the purpose of this discussion, let Impl<\/code> be the class you wrote that implements a Windows Runtime object. If you are implementing something that was declared in an IDL file, it will be the winrt::Namespace::implementation::ClassName<\/code> for the instance object or it will be the winrt::Namespace::factory_implementation::ClassName<\/code> for the factory object. If it wasn’t declared in an IDL file, then it is the class that you manually derived from winrt::implements<\/code>.<\/p>\n

One way to create the object is to use make<Impl><\/code>, which creates the implementation object and then returns the Windows Runtime projection version of that object. (If Impl<\/code> is manually-derived from winrt::implements<\/code>, the projection is the first implemented interface.)<\/p>\n

From that Windows Runtime projection, you can regain access to the implementation object by doing get_self<Impl>(projected)<\/code>, if you want to access things in the implementation object that aren’t exposed in the projection.<\/p>\n

Alternatively, you use make_self<Impl><\/code>, which creates the object but returns a winrt::com_ptr<Impl><\/code> instead of a projection. You can then access things in the implementation object from that winrt::com_ptr<\/code>, and convert it to the projected type with the *<\/code> operator.<\/p>\n\n\n\n\n\n\n
make<\/tt><\/td>\n <\/td>\nmake_self<\/tt><\/td>\n<\/tr>\n
\u2193<\/td>\n <\/td>\n\u2193<\/td>\n<\/tr>\n
projection<\/td>\nget_self<\/tt>
\n\u2192<\/td>\n		implementation<\/td>\n<\/tr>\n
\u2190
\noperator*<\/tt><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Which one you choose depends on where you want to go first.<\/p>\n

If you are first going to access non-projected public members of the implementation class<\/a>, use the -><\/code> operator on the com_ptr<Impl><\/code>. For example, you might want to set up the object before returning the projection.<\/p>\n

winrt::IVector<winrt::Widget>\r\n    MakeWidgets(int style, int count)\r\n{\r\n    std::vector<winrt::Widget> v(count, nullptr);\r\n    std::generate(v.begin(), v.end(), [&] {\r\n        auto widget = winrt::make_self<implementation::Widget>(style);<\/span>\r\n        widget->Enabled(true);                                        <\/span>\r\n        return *widget;\r\n    });\r\n    return winrt::multi_threaded_vector(std::move(v));\r\n}\r\n<\/pre>\n
But if you are just going to use the projection, you can take the direct route instead of going the long way.<\/p>\n
\/\/ The long way\r\n\r\nwinrt::IVector<winrt::Widget>\r\n    MakeWidgets(int style, int count)\r\n{\r\n    std::vector<winrt::Widget> v(count, nullptr);\r\n    std::generate(v.begin(), v.end(), [&] {\r\n        auto widget = winrt::make_self<implementation::Widget>(style);<\/span>\r\n        return *widget;\r\n    });\r\n    return winrt::multi_threaded_vector(std::move(v));\r\n}\r\n<\/pre>\n\n\n\n\n\n\n\n
 <\/td>\n <\/td>\nmake_self<\/tt><\/td>\n<\/tr>\n
 <\/td>\n <\/td>\n\u2193<\/td>\n<\/tr>\n
projection<\/td>\n\u2190
\noperator*<\/tt><\/td>\n		implementation<\/td>\n<\/tr>\n
\u2193<\/td>\n <\/td>\n <\/td>\n<\/tr>\n
returned<\/td>\n <\/td>\n <\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
In this case, you don’t need to pass through the implementation type.<\/p>\n
\/\/ The short way\r\n\r\nwinrt::IVector<winrt::Widget>\r\n    MakeWidgets(int style, int count)\r\n{\r\n    std::vector<winrt::Widget> v(count, nullptr);\r\n    std::generate(v.begin(), v.end(), [&] {\r\n        return winrt::make_self<implementation::Widget>(style);\r\n    });\r\n    return winrt::multi_threaded_vector(std::move(v));\r\n}\r\n<\/pre>\n\n\n\n\n\n\n\n
make<\/tt><\/td>\n<\/tr>\n
\u2193<\/td>\n<\/tr>\n
projection<\/td>\n<\/tr>\n
\u2193<\/td>\n<\/tr>\n
return<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
My guess is that the people who go the long way don’t realize that there are two ways. They learned only one way and just rely on it even if there’s a shorter way.<\/p>\n","protected":false},"excerpt":{"rendered":"
You are taking the scenic route.<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-112803","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
You are taking the scenic route.<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/112803","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=112803"}],"version-history":[{"count":1,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/112803\/revisions"}],"predecessor-version":[{"id":112804,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/112803\/revisions\/112804"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=112803"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=112803"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=112803"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}