The goal of MFC is to make it as easy as possible for C++ developers to create robust Windows applications without sacrificing application performance. For that reason, the MFC class wrappers around the Windows API are, by design, wide and shallow. In other words, although it encapsulates many different APIs, the abstraction layer between the MFC classes and the native Win32 functions under the hood is noticeably thin. For example, the CWnd::SendMessage function does nothing more than call the SendMessage function exposed by the Windows API. Although this approach is frustrating to some developers—especially those who want to develop Windows-based applications without having to invest the time to understand the ins and outs of the Windows programming model—it is most often a good trade-off. It simplifies application development without selling out on speed. Of course, applications built using MFC will suffer some performance penalty compared to those built with the raw Windows API, but for robust, large-scale applications, the maintainability of MFC code more than makes up for any slowdown in speed.
Unfortunately, MFC support for OLE and COM doesn't follow the same model as its support for the Windows API. Although MFC's window classes contain a substantial number of inline wrappers (à la CWnd::SendMessage), its OLE classes aren't nearly as lightweight. As a result, MFC is less suited for middle-tier COM object development than it is for Windows development or even OLE development. Until recently, the COM limitations of MFC have been largely forgivable—ActiveX controls developed with MFC are perfectly adequate for use in end-user applications written in Visual Basic and MFC. And when it comes to traditional OLE support—OLE document servers, compound documents, containers, and so on—MFC is the best choice. However, the recent trend toward client/server Internet applications and the three-tier architecture described earlier has exposed two problems. First, even the smallest components created using MFC are generally considered too large for use within a Web browser, especially considering the time it takes to download the associated DLLs. Second, MFC is not well suited for creating server components that provide no user interface but must simultaneously support multiple threads of execution. Thus, whereas MFC still has something to offer future Windows applications, it falls short when it comes to developing COM objects in the business services tier.