Returning Closures

Return closures from functions using impl Fn or Box.

Difficulty

Advanced

Code

fn make_greeting(name: String) -> impl Fn() {
    move || println!("Hello, {}!", name)
}

fn make_operation(op: &str) -> Box<dyn Fn(i32, i32) -> i32> {
    match op {
        "add" => Box::new(|a, b| a + b),
        "mul" => Box::new(|a, b| a * b),
        _ => Box::new(|a, b| a - b),
    }
}

fn main() {
    let greet = make_greeting(String::from("Rust"));
    greet();

    let add = make_operation("add");
    println!("result: {}", add(3, 5));
}

Explanation

This example demonstrates how to use returning closures in Rust. Read the code carefully to understand the flow. Pay attention to where values are created, borrowed, moved, or consumed.

Key Concepts

• Rust's strong type system catches errors at compile time
• Ownership and borrowing rules ensure memory safety
• Pattern matching makes code expressive and exhaustive

Related Topics

Browse more examples in the functions category to build a complete understanding of this topic.