Understanding Rust Error E0263

Introduction to Rust Error E0263

Rust error E0263 occurs when a lifetime is declared more than once in the same scope. This error code is no longer emitted by the compiler but understanding the reasoning behind it can still be useful for learning Rust lifetimes.

Example of Erroneous Code

#![allow(unused)]
fn main() {
    fn foo<'a, 'b, 'a>(x: &'a str, y: &'b str, z: &'a str) { // error!
    }
}

In the above example, two lifetimes ('a) are declared. This is not valid in Rust.

Fixing the Error

To fix Rust error E0263, simply change the name of one of the conflicting lifetimes to a different name, like 'c for example:

#![allow(unused)]
fn main() {
    fn foo<'a, 'b, 'c>(x: &'a str, y: &'b str, z: &'c str) { // ok!
    }
}

After making the fix, the code will now compile without any errors.

Understanding Lifetimes in Rust

Lifetimes in Rust are used to express how long references should be valid for. When you're specifying lifetimes, you're essentially telling the Rust compiler how long a reference should be valid for. In our example, we use lifetimes to indicate the relationships between the input variables x, y, and z for the function foo.

Conclusion