Not defending "undefined" here, at all. I'd rather see the definition be, at least, exit(0xff) (or some other mechanism that reliably denotes "method not found"

Not defending "undefined" here, at all. I'd rather see the definition be, at least, exit(0xff) (or some other mechanism that reliably denotes "method not found", "message not found", etc). I'm pretty sure I'm on record in HN for ranting about the fact that C & C++'s undefined & funny behavior literally created multimillion dollar industries in building analysis tools to cove their gaping problems. Which is why I am tend to boost Rust when possible (designed for correctness and determinism! woo!). Dropping errors is not IMO better or worse. Both are silent failure modes.