Microsoft Interface Definition Language 3.0 reference

Microsoft Interface Definition Language (MIDL) 3.0 is a simplified, modern, familiar syntax for defining Windows Runtime types inside Interface Definition Language (.idl) files.

// BookSku.idl
namespace Bookstore
    runtimeclass BookSku
        String Title;

As of version 10.0.17134.0 (Windows 10, version 1803), the Windows SDK includes command-line support for MIDL 3.0 (midl.exe version 8.01.0622 or later, used with the /winrt switch).

Topic Description
Introduction to MIDL 3.0 An introduction to Microsoft Interface Definition Language 3.0.
Synthesizing interfaces (MIDL 3.0) This topic describes how the MIDL 3.0 compiler synthesizes and adds interfaces, as necessary.
Predefined attributes (MIDL 3.0) There are a number of pre-defined custom attributes that allow you to control the name and IID for compiler-synthesized interfaces.
Advanced topics, and shorthand Advanced topics, and shorthand syntax.
Transition to MIDL 3.0 from classic MIDLRT MIDL 3.0 can coexist in the same source file with classic MIDLRT; this topic shows how to transition to MIDL 3.0 from MIDLRT.
Reserved keywords (MIDL 3.0) This topic lists the reserved keywords in MIDL 3.0. You may not use these keywords in the names of your runtime classes and members.
Troubleshooting MIDL 3.0 issues A table of troubleshooting symptoms and remedies.