I'm a little dubious of the speed advantage to be honest. Sure compile time is important, and C++ is pretty bad on this front, but you don't need to try that ha

I'm a little dubious of the speed advantage to be honest. Sure compile time is important, and C++ is pretty bad on this front, but you don't need to try that hard to do better. And no, I don't think sum types would slow the compiler down much, especially if they were limited to a special case for error handling (which seems more in line with the rest of Go).