Comment by _0w8t

A common problem with Docker is after running a compiler/preprocessor during an image build one ends up with the bulid tools inside the image. A workaround is to use a shell script that first gets the image with the compiler, run it and then pass the output to the Docker build. But this is non-standard and encourages running random scripts on the build host defeating the advantages of using Docker during development to isolate build system. It is nice that Nix addresses this.