Advanced
Rust
Q60 / 100
What is variance in Rust lifetimes?
Correct! Well done.
Incorrect.
The correct answer is B) Whether substituting a subtype for a type parameter is allowed: covariant (safe to substitute longer), contravariant (shorter), or invariant (exact)
B
Correct Answer
Whether substituting a subtype for a type parameter is allowed: covariant (safe to substitute longer), contravariant (shorter), or invariant (exact)
Explanation
&'a T is covariant over 'a and T. &'a mut T is covariant over 'a but invariant over T (to prevent unsound mutations). PhantomData affects variance.
Progress
60/100