Memory Safety in Rust

fn main() {
    println!("Hello, world!");
    println!("Let's try to overflow the buffer!");

    let array = [0, 0, 0, 0, 0];

    // This would cause a compile error or panic
    for index in 0..10 {
        println!("Index {}: {}", index, array[index]); // Panic on out of bounds
    }
}

fn main() {
    // Ownership example 1: Simple ownership transfer
    let s1 = String::from("hello");
    let s2 = s1; // s1 is moved to s2, s1 is no longer valid

    // println!("{}", s1); // This would cause a compile error!
    println!("s2: {}", s2); // This works fine

    // Ownership example 2: Automatic cleanup
    {
        let s3 = String::from("world");
        println!("s3: {}", s3);
    } // s3 goes out of scope here and memory is automatically freed

    // Ownership example 3: Preventing double-free
    let s4 = String::from("rust");
    let s5 = s4.clone(); // Clone creates a deep copy, both s4 and s5 are valid
    println!("s4: {}, s5: {}", s4, s5);

    // Both s4 and s5 will be automatically dropped when they go out of scope
}

fn main() {
    // Ownership example 1: Simple ownership transfer
    let s1 = String::from("hello");
    let s2 = s1; // s1 is moved to s2, s1 is no longer valid

    //println!("{}", s1); // This would cause a compile error!
    println!("s2: {}", s2); // This works fine

    let k1 = 20;
    let k2 = k1;

    println!("k1 {}", k1); // This works fine
    println!("k2: {}", k2); // This works fine
}

// Copy vs Move demonstration
fn main() {
    // String - Move semantics (no Copy trait)
    let s1 = String::from("hello");
    let s2 = s1; // Move: s1 is moved to s2
    // s1 is now invalid, s2 owns the data

    // Integer - Copy semantics (has Copy trait)
    let n1 = 42;
    let n2 = n1; // Copy: n1 is copied to n2
    // Both n1 and n2 are valid and independent

    println!("n1: {}, n2: {}", n1, n2); // Both work fine

    // Other Copy types include: i32, f64, bool, char, tuples of Copy types
    let b1 = true;
    let b2 = b1; // Copy
    println!("b1: {}, b2: {}", b1, b2); // Both work fine
}

// Ownership in functions
fn take_ownership(s: String) {
    println!("I own this string: {}", s);
} // s goes out of scope and is dropped

fn make_copy(i: i32) {
    println!("I copied this integer: {}", i);
} // i goes out of scope, but i32 is Copy so no cleanup needed

fn main() {
    let s = String::from("hello");
    take_ownership(s); // s is moved into the function
    // println!("{}", s); // Error! s is no longer valid

    let x = 5;
    make_copy(x); // x is copied into the function
    make_copy(x); // x is copied into the function
    println!("x is still valid: {}", x); // x is still valid
}

fn main() {
    let mut data = vec![1, 2, 3, 4, 5];

    // Multiple immutable references allowed
    let r1 = &data;
    let r2 = &data;
    let r3 = &data;
    println!("r1: {:?}", r1);
    println!("r2: {:?}", r2);
    println!("r3: {:?}", r3);

    // Drop immutable references before creating mutable one
    let _ = r1;
    let _ = r2;
    let _ = r3;

    // Only one mutable reference allowed
    let r4 = &mut data;
    r4.push(6);
    println!("r4: {:?}", r4);

    // This would cause a compile error:
    // let r5 = &data; // Error: cannot borrow as immutable
    // let r6 = &mut data; // Error: cannot borrow as mutable
    // println!("{:?} {:?}", r5, r6);

    demonstrate_borrowing();
}

// Example: Function that reads data
fn read_data(data: &Vec<i32>) {
    println!("Reading data: {:?}", data);
}

// Example: Function that modifies data
fn modify_data(data: &mut Vec<i32>) {
    data.push(42);
}

fn demonstrate_borrowing() {
    let mut numbers = vec![1, 2, 3];

    read_data(&numbers); // Immutable borrow
    modify_data(&mut numbers); // Mutable borrow
    read_data(&numbers); // Immutable borrow again

    println!("Final: {:?}", numbers);
}

// Example 1: Lifetime annotations in structs
struct Person<'a> {
    name: &'a str,
    age: u32,
}

fn main() {
    let name = String::from("Alice");

    let person = Person {
        name: &name, // Reference must live as long as Person
        age: 30,
    };

    println!("Name: {}, Age: {}", person.name, person.age);
} // name and person go out of scope safely

// Example 2: Function with lifetime parameters
fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
    if x.len() > y.len() { x } else { y }
}

fn demonstrate_longest() {
    let string1 = String::from("short");
    let string2 = String::from("longer string");

    let result = longest(&string1, &string2);
    println!("The longest string is: {}", result);

    // Both string1 and string2 must live at least as long as result
}

// Example 3: Lifetime elision (compiler infers lifetimes)
fn first_word(s: &str) -> &str {
    let bytes = s.as_bytes();

    for (i, &item) in bytes.iter().enumerate() {
        if item == b' ' {
            return &s[0..i];
        }
    }

    &s[..]
}

// Example 4: Preventing dangling references
fn create_reference() -> &'static str {
    "This is a static string" // 'static lifetime - lives for entire program
}

// This would NOT compile (dangling reference):
/*
fn bad_function() -> &str {
    let s = String::from("hello");
    &s // Error: s goes out of scope, but reference would remain
}
*/

fn main() {
    let arr = [1, 2, 3, 4, 5];

    // Example 1: Safe indexing with get()
    match arr.get(2) {
        Some(value) => println!("Index 2: {}", value),
        None => println!("Index 2: Out of bounds!"),
    }

    match arr.get(10) {
        Some(value) => println!("Index 10: {}", value),
        None => println!("Index 10: Out of bounds!"),
    }

    // Example 2: Direct indexing (panics on out of bounds)
    println!("Index 1: {}", arr[1]); // Safe: within bounds

    // This would panic at runtime:
    // println!("Index 10: {}", arr[10]); // Panic: index out of bounds

    // Example 3: Safe iteration
    for (i, &value) in arr.iter().enumerate() {
        println!("Index {}: {}", i, value);
    }

    // Example 4: Working with slices
    let slice = &arr[1..4]; // Safe slice creation
    println!("Slice: {:?}", slice);

    // Example 5: Safe array access in loops
    let indices = [0, 2, 4, 6]; // Some indices are out of bounds
    for &index in &indices {
        match arr.get(index) {
            Some(val) => println!("arr[{}] = {}", index, val),
            None => println!("arr[{}] is out of bounds", index),
        }
    }
}

// Example 6: Function that safely processes array data
fn safe_process_array(arr: &[i32]) {
    for i in 0..10 { // Try to access indices 0-9
        match arr.get(i) {
            Some(value) => println!("Processing value {} at index {}", value, i),
            None => {
                println!("Stopping at index {} (out of bounds)", i);
                break;
            }
        }
    }
}

// Example 1: No null pointer dereferencing with Option<T>
fn find_user(id: u32) -> Option<String> {
    if id == 1 {
        Some("Alice".to_string())
    } else {
        None // No null pointer, just None
    }
}

fn main() {
    let user = find_user(1);

    match user {
        Some(name) => println!("Found user: {}", name),
        None => println!("User not found"),
    }

    // Safe unwrapping with defaults
    let user_name = user.unwrap_or("Unknown".to_string());
    println!("User name: {}", user_name);
}

// Example 2: Type safety with Result<T, E> for error handling
fn divide(a: i32, b: i32) -> Result<i32, String> {
    if b == 0 {
        Err("Division by zero".to_string())
    } else {
        Ok(a / b)
    }
}

fn demonstrate_result() {
    let result = divide(10, 2);
    match result {
        Ok(value) => println!("Result: {}", value),
        Err(error) => println!("Error: {}", error),
    }

    let bad_result = divide(10, 0);
    match bad_result {
        Ok(value) => println!("Result: {}", value),
        Err(error) => println!("Error: {}", error),
    }
}

// Example 4: Type safety with enums
enum Message {
    Text(String),
    Number(i32),
    Empty,
}

fn process_message(msg: Message) {
    match msg {
        Message::Text(text) => println!("Text message: {}", text),
        Message::Number(num) => println!("Number message: {}", num),
        Message::Empty => println!("Empty message"),
    }
}

fn main() {
    // Example 1: Move semantics prevent accidental deep copies
    let data1 = vec![1, 2, 3, 4, 5]; // Vec allocates memory on heap
    let data2 = data1; // Move: data1 is moved to data2 (no deep copy!)

    // println!("{:?}", data1); // Error! data1 is no longer valid
    println!("data2: {:?}", data2); // data2 now owns the data

    // In C++, this would be: Vec<int> data2 = data1; // Expensive deep copy!
    // In Rust, this is just a pointer move - O(1) operation

    // Example 2: Move semantics with large data structures
    let large_string1 = "A".repeat(1000000); // 1MB string
    let large_string2 = large_string1; // Move: just pointer transfer, no copying!

    println!("String length: {}", large_string2.len());
    // No performance cost - just moved the ownership

    // Example 3: Move semantics in function calls
    let expensive_data = vec![1; 1000000]; // Large vector

    process_data(expensive_data); // Moved into function, no copy
    // expensive_data is no longer valid here

    // If we wanted to keep it, we'd need to clone:
    let another_data = vec![2; 1000000];
    process_data(another_data.clone()); // Expensive deep copy
    println!("Still have: {:?}", another_data); // Still valid
}

fn process_data(data: Vec<i32>) {
    println!("Processing {} elements", data.len());
    // data is dropped here when function ends
}

// Example 4: Move semantics enable zero-cost abstractions
fn main() {
    let numbers = vec![1, 2, 3, 4, 5];

    // This iterator chain doesn't copy the data multiple times
    let result: Vec<i32> = numbers
        .into_iter()        // Move numbers into iterator
        .map(|x| x * 2)     // Transform each element
        .filter(|&x| x > 5) // Filter elements
        .collect();         // Collect into new Vec

    println!("Result: {:?}", result);

    // numbers is moved and no longer available
    // Each transformation is applied lazily without copying
}

// Example 5: Preventing accidental deep copies
fn demonstrate_copy_vs_move() {
    let original = vec![1, 2, 3];

    // Move semantics - no copy
    let moved = original; // original is no longer valid
    println!("Moved: {:?}", moved);

    // If we need a copy, we must be explicit
    let copied = moved.clone(); // Explicit deep copy
    println!("Original moved: {:?}", moved); // Still valid
    println!("Copy: {:?}", copied); // Independent copy

    // This prevents expensive accidental copies
}