I agree that you could reduce the lines of code by modernizing, and get more reliable code (the current codebase has cases of UB that they neglected pull requests to fix for a year and counting, see https://github.com/milkytracker/MilkyTracker/pull/255 and https://github.com/milkytracker/MilkyTracker/pull/256). But MilkyTracker is uniquely fast in compiling, I think because of avoiding STL and heavyweight headers. My hope is that in the future we can have container niceties and lightning-fast compilation (perhaps modules over headers, concepts over SFINAE, or using STL alternative containers designed to be lightweight like EASTL or Corrade, or jumping ship from C++ entirely to Zig or Nim or so).
Probably you could speed up the build by consolidating it into a few files; linking is about the slowest thing compilers do, although mold could help, there.
Moving small things into headers might seem like it would slow down the build, but anything wholly defined in a header doesn't need to be linked.
Looking at your pull 256, a delegating constructor would seem to be right thing, but initializing in the class declaration is absolutely best. I wonder who still wants it pre-C++11.
