Inferring lifetimes from the implementation of a function won't happen for the same reason that inferring types won't happen: it is really nice for the signatur

Inferring lifetimes from the implementation of a function won't happen for the same reason that inferring types won't happen: it is really nice for the signature of a function to not automatically be changed if the body is changed, instead programmers should be told when they might be breaking their users. However, the compiler could (and did, I believe) run inference and suggest a fix that the programmer can explicitly include.