Rust for C-Programmers

21.16 If Let Chains (Planned for the Rust 2024 Edition)

A new feature called if-let chains is planned for inclusion in Rust 2024, enhancing the expressiveness of conditional pattern matching. This feature allows multiple if let conditions to be combined in a single statement using logical && (AND) or || (OR) operators, reducing the need for deeply nested conditional structures.

21.16.1 Why If Let Chains?

Traditionally, handling multiple if let conditions required nesting or separate checks, which could make the code less readable. With if-let chains, Rust allows multiple pattern matches in a single if condition, making the code more concise and clear.

21.16.2 Example Usage

The following example demonstrates if-let chains in action. It requires the nightly compiler and must include the #![feature(let_chains)] directive to enable this experimental feature:

#![feature(let_chains)]

fn main() {
    let some_value: Option<i32> = Some(42);
    let other_value: Result<&str, &str> = Ok("Success");

    if let Some(x) = some_value && let Ok(y) = other_value {
        println!("Matched! some_value: {}, other_value: {}", x, y);
    } else {
        println!("No match!");
    }
}

21.16.3 Compiling and Running the Example

Since this feature is currently unstable, it requires a nightly Rust compiler. To compile and run the example, use the following commands:

rustup override set nightly  # Enable nightly Rust in the project directory
cargo build                  # Compile the project
cargo run                    # Run the program

Alternatively, for a one-time compilation with nightly Rust:

cargo +nightly build

21.16.4 Expected Output

Matched! some_value: 42, other_value: Success

21.16.5 Feature Status

• Nightly Only: This feature is still under development and requires explicit activation via #![feature(let_chains)].
• Planned for Rust 2024: If stabilized, it will become part of Rust 2024, eliminating the need for the feature flag.

By allowing multiple conditional matches in a single if statement, if-let chains improve code readability and reduce unnecessary nesting. Once stabilized, this feature will offer a more elegant approach to handling multiple pattern matches in Rust programs.