Week 3: Ownership as a foil

Rust's borrow checker as the design target every C retrofit in this course gets measured against, even though it isn't itself a C tool

8 March 2027

Rust doesn’t appear on the syllabus after this week, and it’s the only lecture where the tool under discussion can’t be applied to a line of C. It’s here anyway, because every retrofit from week 4 onward is implicitly answering the question “how much of what Rust gets for free can you claw back inside a language that was never going to have it built in?”

Ownership types give you spatial and temporal memory safety as a static, sound, zero-runtime-cost property of the type system — at the cost of a much more restrictive language, and years of programmer retraining. That cost is exactly what the rest of this course is about: no C retrofit gets that whole guarantee, and each one is legible as a specific, deliberate partial refund.

Outline#

• ownership, borrowing, and lifetimes as a static answer to aliasing
• what “zero-cost abstraction” actually costs (compile time, expressiveness, the learning curve)
• why this can’t just be bolted onto C: the guarantee needs the type system to have been designed around it from the start
• the framing for the rest of semester: each retrofit as a point in the design space between “no safety, full C” and “full safety, not C anymore”