I don't consider this a semantic argument. The exact same code, without the transmute (just returning x directly from an unsafe block), fails a type check rela

I don't consider this a semantic argument. The exact same code, without the transmute (just returning x directly from an unsafe block), fails a type check related to borrowing. Specifically, the compiler can't see why (without a transmute) it should believe that the reference x now has a different lifetime 'b instead of 'a. Which is fair because it doesn't. The transmute is you claiming it does, and since transmute is an unsafe function that's entirely on you to make sure you're right about that. So, lying has the expected effect. The borrow checks aren't magic, they can't look into your soul - but they are running inside unsafe code too. * Edited to make explicit that the alternative is still marked unsafe and yet doesn't work