I was able to use casting pointer (rather unsafely I believe) for some
dependency injection, but that's only because it relies on the builder being
defined inline to the shape:

https://github.com/mattsah/mininim-core/blob/main/src/mininim/dic.nim

Used here:

https://github.com/mattsah/mininim-cli/blob/main/src/mininim/cli.nim