一名C++程式員的Rust入門初體驗

let x = 0;
x = 10;  // error

let mut y = 0;
y = 10;  //ok

fn foo(x: u32) {}

let x: i32 = 0;
foo(x);  // error

class ABC
{
public:
    virtual ~ABC();

    ABC(const ABC&) = delete;
    ABC(ABC&&) = delete;

    ABC& operator=(const ABC&) = delete;
    ABC& operator=(ABC&&) = delete;
};

fn main()
{
    // String類似std::string，只支持顯式clone，不支持隱式copy
    let s: String = "str".to_string();
    
    foo(s);  // s will move
    // cannot use s anymore

    let y = "str".to_string();
    foo(y.clone());

    // use y is okay here
}

fn foo(s: String) {}

// can only be passed by move
struct Abc1
{
    elems: Vec<int>
}

// can use abc.clone() to explicit clone a new Abc
#[derive(Clone)]
struct Abc2
{
    elems: Vec<int>
}

// implement custom destructor for Abc
impl Drop for Abc2 {
    // ...
}

// foo(xyz) will copy, 不能再定義Drop/析構函數，因為copy和drop是互斥的
#[dervie(Clone, Copy)]
struct Xyz
{
    elems: i32
}

let mut x = 10;

foo(x);  // pass by move, x cannot be used after the call
foo(&x);  // pass by immutable reference
foo(&mut x); // pass by mutable reference

enum MyError
{
    NotFound,
    DataCorrupt,
    Forbidden,
    Io(std::io::Error)
}

impl From<io::Error> for MyError {
    fn from(e: io::Error) -> MyError {
        MyError::Io(e)
    }
}

pub type Result<T> = result::Result<T, Error>;

fn main() -> Result<()>
{
    let x: i32 = foo()?;
    let y: i32 = bar(x)?;

    foo();  // result is not handled, compile error

     // use x and y
}

fn foo() -> Result<i32>
{
    if (rand() > 0) {
        Ok(1)
    } else {
        Err(MyError::Forbidden)
    }
}

cargo test
cargo bench

benches  // benchmark代碼go here
src
tests  // ut go here

let s = vec![1,2,3];  // s owns the Vec
foo(s);  // the ownership is passed to foo, s cannot be used anymore

let x = vec![1,2,3];
let a1 = &x[0];
let a2 = &x[0];  // a1/a2 are both immutable ref to x

x.resize(10, 0);  // error: x is already borrowed by a1 and a2

println!("{a1} {a2}");

let s: &String;

{
    let x = String::new("abc");
    s = &x;
}

println!("s is {}", s);  // error, lifetime(s) > lifetime(x)

// not valid rust, for exposition only
struct ABC
{
    x: &String,
}

fn foo(x: String)
{
    let z = ABC { x: &x };

    consume_string(x);  // not compile, x is borrowed by z
    drop(z);  // call destructor explicitly

    consume_string(x);  // ok

    // won't compile, bind a temp to z.x
    let z = ABC { x: &String::new("abc") };
    // use z

    // Box::new == make_unique
    // won't compile, the box object is destroyed soon
    let z = ABC{ x: &*Box::new(String::new("abc") };
    // use z
}

void foo(ThreadPool* thread_pool)
{
    Latch latch{2};

    thread_pool->spawn([&latch] {
        // ...
        latch.wait();  // dangle pointer訪問
    });

    // forget latch.wait();
}

fn foo(thread_pool: &mut ThreadPool)
{
    let latch = Arc::new(Latch::new(2));
    let latch_copy = Arc::clone(&latch);

    thread_pool.spawn(move || {
        // the ownership of latch_copy is moved in
        latch_copy.wait();
    });

    latch.wait();
}

FileLineReader reader(path);

std::string_view<char> line = reader.NextLine();
std::string_view<char> line2 = reader.NextLine();

// ops
std::cout << line;

let reader = FileReader::next(path);
let line = reader.next_line();

// won't compile, reader is borrowed to line, cannot mutate it now
let line2 = reader.next_line();

println!("{line}");

// &[u8] is std::span<byte>
fn foo() -> &[u8] {
    let reader = FileReader::next(path);
    let line = reader.next_line();

    // won't compile, lifetime(line) > lifetime(reader)
    return line;
}

let i: i32;

if rand() < 10 {
    i = 10;
}

println!("i is {}", i);  // do not compile: i is not always initialized

struct Counter
{
    counter: i32
}

fn main()
{
    let counter = Arc::new(Counter{counter: 0});
    let c = Arc::clone(&counter);
    thread::spawn(move || {
        c.counter += 1;
    });

    c.counter += 1;
}

fn main()
{
    let counter = Arc::new(RefCell::new(Counter{counter: 0}));
    let c = Arc::clone(&counter);
    thread::spawn(move || {
        c.get_mut().counter += 1;
    });

    c.get_mut().counter += 1;
}

struct Counter
{
    counter: i32
}

fn main()
{
    let counter = Arc::new(Mutex::new(Counter{counter: 0}));
    let c = Arc::clone(&counter);
    thread::spawn(move || {
        let mut x = c.lock().unwrap();

        x.counter += 1;
    });
}

// for demo purpose

fn foo(tasks: Vec<Task>)
{
    let latch = Arc::new(Latch::new(tasks.len() + 1));

    for task in tasks {
        let latch = Arc::clone(&latch);
        thread_pool.submit(move || {
            task.run();
            latch.wait();
        });
    }

    latch.wait();
}

int foo(const int* x, int* y)
{
    *y = *x + 1;

     return *x;
}

fn foo(x: &i32, y: &mut i32) -> i32
{
    *y = *x + 1;

    *x
}

# c++
__Z3fooPKiPi:
    ldr    w8, [x0]
    add    w8, w8, #1
    str    w8, [x1]
    ldr    w0, [x0]
    ret

# rust
__ZN2rs3foo17h5a23c46033085ca0E:
    ldr    w0, [x0]
    add    w8, w0, #1
    str    w8, [x1]
    ret