Closures as Win32 window procedures

Back in 2017 I wrote about a technique for creating closures in C using JIT-compiled wrapper. It’s neat, though rarely necessary in real programs, so I don’t think about it often. I applied it to qsort, which sadly accepts no context pointer. More practical would be working around insufficient custom allocator interfaces, to create allocation functions at run-time bound to a particular allocation region. I’ve learned a lot since I last wrote about this subject, and a recent article had me thinking about it again, and how I could do better than before. In this article I will enhance Win32 window procedure callbacks with a fifth argument, allowing us to more directly pass extra context. I’m using w64devkit on x64, but the everything here should work out-of-the-box with any x64 toolchain that speaks GNU assembly.
↫ Chris Wellons

Sometimes, people get upset when I mention something is out of my wheelhouse, so just for those people, here’s an article well outside of my wheelhouse. I choose honesty over faking confidence.