while let Statements

Like with if let, there is a while let variant that repeatedly tests a value against a pattern:

# // Copyright 2025 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
fn main() {
    let mut name = String::from("Comprehensive Rust 🦀");
    while let Some(c) = name.pop() {
        dbg!(c);
    }
    // (There are more efficient ways to reverse a string!)
}

Here String::pop returns Some(c) until the string is empty, after which it will return None. The while let lets us keep iterating through all items.

• Point out that the while let loop will keep going as long as the value matches the pattern.
• You could rewrite the while let loop as an infinite loop with an if statement that breaks when there is no value to unwrap for name.pop(). The while let provides syntactic sugar for the above scenario.
• This form cannot be used as an expression, because it may have no value if the condition is false.