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Hello world!

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Reza

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fn main() {
    // Ownership: Each value has a single owner
    let s1 = String::from("hello");
    
    // Move semantics: ownership transferred to s2
    let s2 = s1;
    // println!("{}", s1); // Compile error: value moved
    println!("s2 owns: {}", s2);
    
    // Clone for deep copy when needed
    let s3 = s2.clone();
    println!("s2: {}, s3: {}", s2, s3);
    
    // Borrowing: immutable references
    let len = calculate_length(&s3);
    println!("Length of '{}' is {}", s3, len);
    
    // Mutable borrowing: exclusive access
    let mut s4 = String::from("hello");
    append_world(&mut s4);
    println!("After mutation: {}", s4);
    
    // Multiple immutable borrows allowed
    let r1 = &s4;
    let r2 = &s4;
    println!("r1: {}, r2: {}", r1, r2);
    
    // Demonstrates non-lexical lifetimes (NLL)
    {
        let r3 = &s4;
        println!("r3: {}", r3);
    } // r3 scope ends, can now mutably borrow
    
    let r4 = &mut s4;
    r4.push_str("!");
    println!("Final: {}", r4);
}

fn calculate_length(s: &String) -> usize {
    s.len()
    // s goes out of scope but doesn't drop the String
    // because it doesn't have ownership
}

fn append_world(s: &mut String) {
    s.push_str(", world");
    // Mutable reference allows modification
}

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