Lifetimes
⚑ Report an issue with this lessonLifetimes tell the compiler how long references stay valid, so it can catch dangling references before your program ever runs:
fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
if x.len() > y.len() { x } else { y }
}The 'a here says: the returned reference lives at most as
long as the shorter of the two input lifetimes. Most of the time the
compiler infers lifetimes for you -- you only write them explicitly when a
function's signature is ambiguous about how long its inputs and outputs
relate.
Try it yourself
Exercise: The longest function below will not compile because the compiler cannot tell how the lifetimes of x, y, and the return value relate. Add the correct lifetime annotation (like 'a) to the signature so it compiles, then complete the body to return the longer of x and y. Call it with "hello" and "hi" and print the result.
Expected output:
hello
Run your code and get it working before marking this lesson complete.
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