Rust is a systems programming language that offers performance comparable to C and C++ with memory safety and thread safety. It uses a borrow checker to enforce rules around ownership, borrowing, and lifetimes that prevent common bugs like use of dangling pointers and data races. Rust also supports features like generics, pattern matching, and idioms that improve productivity without sacrificing performance.

1. An introduction to rust
Performance. Reliability. Productivity.
Cyril Soldani
University of Liège
22nd of February 2019
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2. Outline
1 Why?
2 What?
3 Discussion
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3. Outline
1 Why?
2 What?
3 Discussion
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4. Rust fits an interesting niche
System programming is needed for:
low-level stuff like Operating Systems;
applications that need to run fast;
cheap/efficient embedded systems.
Your python toolkit runs more C/C++/Fortran than python!
Although everything else relies on it, system programming is
notoriously error-prone!
Rust makes system programming easier and much safer.
But rust is not just for system programming!
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5. Rust is designed for performance
Very much like C++, rust:
is statically typed;
compiles to native executables;
has no runtime;
has no garbage collector;
give you control of memory layout;
integrates easily with C code;
has zero-cost abstractions.
=⇒ Idiomatic rust performance is on par with idiomatic C/C++.
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6. Rust is reliable
If no possible execution can exhibit undefined behaviour, we say
that a program is well-defined.
If a language’s type system enforces that every program is
well-defined, we say it is type-safe.
C/C++ are not type-safe:
char buf[16];
buf[24] = 42; // Undefined behaviour
Rust is type-safe:
Guaranteed memory-safety:
No dereference of null pointers.
No dangling pointers.
No buffer overflow.
Guaranteed thread-safety:
Threads without data races.
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7. Rust is good for productivity
High-level features: traits, pattern matching, closures, etc.
Great documentation.
Good error messages.
Built-in testing tools.
Built-in package manager and build tool (cargo).
Built-in documentation tool.
Good IDE integration (auto-completion, type inspection,
formatting, etc.).
Great community.
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8. Rust is popular
StackOverflow
In 2018 survey: 78.9% of rust users love the language
. . . which makes it the most loved language
. . . for the 3rd year in a row!
GitHub
rust-lang/rust:
1.3k 34k 5.5k 90k 2.3k
4.4k active repositories with rust code.
Still on the rise, gathering momentum!
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9. Rust is mature
History
2006 start of development by G. Hoare (Mozilla Research).
2009 endorsed by Mozilla.
2010 rust is announced.
2011 rustc is self-hosting.
2012 first public release.
2015 first stable release: Rust 1.0.
...
2019 Rust 1.32, development still active!
The language changed a lot in its infancy, but is now rather stable.
Used for various projects by Mozilla, Samsung, Dropbox, NPM,
Oracle, Microsoft, . . .
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10. Outline
1 Why?
2 What?
The borrow checker
Some other language features
3 Discussion
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11. Hello, World!
1 fn main() {
2 // A very original first program
3 println!("Hello, World!");
4 }
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12. A trivial (?) bug
1 vector<int> v;
2 v.push_back(1);
3 int& x = &v[0];
4 v.push_back(2);
5 cout << x << endl;
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13. A trivial (?) bug
1 vector<int> v;
2 v.push_back(1);
3 int& x = &v[0];
4 v.push_back(2); // Re-allocate buffer
5 cout << x << endl;
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14. A trivial (?) bug
1 vector<int> v;
2 v.push_back(1);
3 int& x = &v[0];
4 v.push_back(2); // Re-allocate buffer
5 cout << x << endl; // Dangling pointer!!!
segmentation fault
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15. A trivial (?) bug
1 vector<int> v;
2 v.push_back(1);
3 int& x = &v[0];
4 v.push_back(2); // Re-allocate buffer
5 cout << x << endl; // Dangling pointer!!!
segmentation fault
Problems happen when a resource is both
aliased, i.e. there are multiple references to it;
mutable, i.e. one can modify the resource.
=⇒ restrict mutability or aliasing!
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16. In rust, everything is immutable by default
1 let x = 42;
2 x = 1984;
3 println!("x = {}", x);
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17. In rust, everything is immutable by default
1 let x = 42;
2 x = 1984; // Error!
3 println!("x = {}", x);
error[E0384]: cannot assign twice to immutable variable ‘x‘
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18. In rust, everything is immutable by default
1 let mut x = 42;
2 x = 1984;
3 println!("x = {}", x);
x = 1984
Use mut when something should be mutable.
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19. Ownership
A binding owns the resources it is bound to.
Bound resource is deallocated automatically and
deterministically when its binding goes out of scope.
In a given scope, bindings are freed in LIFO order.
1 {
2 let mut v1 = Vec::new();
3 let mut v2 = Vec::new();
4 // ...
5 // Release v2, then v1
6 }
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20. Move semantics
1 fn eat_vec(v: Vec<i32>) {
2 // ...
3 }
4
5 fn main() {
6 let mut v = Vec::new();
7 v.push(1);
8 eat_vec(v);
9 v.push(2);
10 }
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21. Move semantics
1 fn eat_vec(v: Vec<i32>) {
2 // ..., then release v
3 }
4
5 fn main() {
6 let mut v = Vec::new();
7 v.push(1);
8 eat_vec(v);
9 v.push(2); // Error!
10 }
error[E0382]: use of moved value: ‘v‘
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22. Move semantics
1 fn eat_vec(v: Vec<i32>) {
2 // ..., then release v
3 }
4
5 fn main() {
6 let mut v = Vec::new();
7 v.push(1);
8 eat_vec(v);
9 v.push(2); // Error!
10 }
error[E0382]: use of moved value: ‘v‘
Solutions:
Return value.
Copy value.
Lend value.
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23. Borrowing
1 fn borrow_vec(v: &Vec<i32>) {
2 // ...
3 }
4
5 fn main() {
6 let mut v = Vec::new();
7 v.push(1);
8 borrow_vec(&v);
9 v.push(2);
10 }
&T is a reference.
A reference only borrows ownership, will not deallocate.
Multiple references to same resource is OK.
Explicit for both caller and callee.
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24. Mutable borrow
1 fn mutate_vec(v: &mut Vec<i32>) {
2 v[0] = 42;
3 }
4
5 fn main() {
6 let mut v = Vec::new();
7 v.push(1);
8 mutate_vec(&mut v);
9 v.push(2);
10 }
&mut T is a mutable reference.
There can be only one mutable reference to a resource.
Explicit for both caller and callee.
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25. If a reference is mutable, it is the only reference
1 fn main() {
2 let mut x = 1984;
3 let x_ref_1 = &x;
4 let x_ref_2 = &x; // Multiple refs is OK
5
6 let mut y = 42;
7 let y_mut_ref = &mut y; // OK, single ref
8
9 let mut z = 2001;
10 let z_mut_ref = &mut z; // Error!
11 let z_ref = &z;
12 }
error[E0502]: cannot borrow ‘z‘ as mutable because it is also
borrowed as immutable
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26. If a reference is mutable, it is the only reference
1 fn main() {
2 let mut x = 1984;
3 let x_ref_1 = &x;
4 let x_ref_2 = &x; // Multiple refs is OK
5
6 let mut y = 42;
7 let y_mut_ref = &mut y; // OK, single ref
8
9 let mut z = 2001;
10 let z_mut_ref = &mut z; // Error!
11 let z_ref = &z;
12 }
Note that access through x, y, z is restricted as well.
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27. Rust also tracks the lifetime of resources
2 let x;
3 { // Enter new scope
4 let y = 42;
5 x = &y; // x is a ref to y
6 } // Leave scope, destroy y
7 println!("x = {}", x); // What does x points to?
error[E0597]: `y` does not live long enough
--> test.rs:5:14
|
5 | x = &y; // x is a ref to y
| ˆ borrowed value does not live long enough
6 | } // Leave scope, destroy y
| - `y` dropped here while still borrowed
7 | println!("x = {}", x);
8 | }
| - borrowed value needs to live until here
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28. The compiler can infer lifetimes, but sometimes needs a
little help
1 fn choose(s1: &str, s2: &str) -> &str { s1 }
2
3 fn main() {
4 let s = choose("foo", "bar");
5 println!("s = {}", s);
6 }
error[E0106]: missing lifetime specifier
help: this function’s return type contains a borrowed value, but
the signature does not say whether it is borrowed from ‘s1‘ or ‘s2‘
1 fn choose<'a>(s1: &'a str, s2: &str) -> &'a str
'static is for immortals.
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29. The borrow checker allows for fearless concurrency
1 fn use_lock(mutex: &Mutex<Vec<i32>>) {
2 let vec = {
3 // Acquire the lock
4 let mut guard = lock(mutex);
5 // Attempt to return a borrow of the data
6 access(&mut guard)
7 // Guard is destroyed here, releasing the lock
8 };
9 // Attempt to access the data outside of the lock.
10 vec.push(3); // Error: guard does not live long enough
11 }
Concurrency not only safe but easy:
Locks know their data, which can’t be accidentally shared.
Channels move data between threads.
Many readers, one writer extends to thread-shared data.
You can share even stack frames, without disaster!
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30. Generic functions
1 fn guess_what<T>(x: T) -> T {
2 // ?
3 }
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31. Generic functions
1 fn guess_what<T>(x: T) -> T {
2 // ?
3 }
Parametric types are constrained.
1 fn min<T: Ord>(x: T, y: T) {
2 if x < y { x } else { y }
3 }
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32. Generic functions
1 fn identity<T>(x: T) -> T {
2 x
3 }
Parametric types are constrained.
1 fn min<T: Ord>(x: T, y: T) {
2 if x < y { x } else { y }
3 }
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33. Generic functions
1 fn identity<T>(x: T) -> T {
2 x
3 }
Parametric types are constrained.
1 fn min<T: Ord>(x: T, y: T) {
2 if x < y { x } else { y }
3 }
=⇒ Theorems for free!
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34. Generic types
1 struct Point<T> {
2 x: T,
3 y: T
4 }
5
6 fn main() {
7 let p_f32: Point<f32> = Point { x: 1.2, y: 3.4 };
8 let mut p_i64 = Point { x: 1, y: 2 };
9 let p_i32 = Point { x: 1, y: 2 };
10 let p_f64 = Point { x: 3.14, y: 1.592 };
11
12 p_i64.x = 42i64;
13 }
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35. Enumerations
1 enum Button {
2 Left, Middle, Right,
3 }
4
5 enum Event {
6 Move { x: i32, y: i32 },
7 Click(Button),
8 KeyPress(char),
9 }
10
11 fn main() {
12 let e = Event::Click(Button::Left);
13 }
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36. Pattern matching: efficient and legible if-else-if
1 fn process(e: Event) {
2 use Event::*;
3 match e {
4 KeyPress(c) => println!("Pressed key {}", c),
5 Move {x, y} => {
6 println!("Moved to ({},{})", x, y);
7 }
8 }
9 }
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37. Pattern matching: efficient and legible if-else-if
1 fn process(e: Event) {
2 use Event::*;
3 match e {
4 KeyPress(c) => println!("Pressed key {}", c),
5 Move {x, y} => {
6 println!("Moved to ({},{})", x, y);
7 }
8 }
9 }
error[E0004]: non-exhaustive patterns: ‘Click(_)‘ not covered
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38. Pattern matching: efficient and legible if-else-if
1 fn process(e: Event) {
2 use Event::*;
3 match e {
4 KeyPress(c) => println!("Pressed key {}", c),
5 Move {x, y} => {
6 println!("Moved to ({},{})", x, y);
7 }
8 }
9 }
error[E0004]: non-exhaustive patterns: ‘Click(_)‘ not covered
Filter matches with guards: X(i) if i < 3 =>.
Combine multiple arms with One | Two =>.
Ranges: 12 .. 19 =>.
Bindings: name @ ... =>.
Partial matches with _ and ...
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39. Generic enumerations
1 enum Option<T> {
2 /// No value
3 None,
4 /// Some value `T`
5 Some(T),
6 }
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40. Generic enumerations
1 enum Option<T> {
2 /// No value
3 None,
4 /// Some value `T`
5 Some(T),
6 }
Option used for optional values, partial functions, etc. No NULL!
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41. Generic enumerations
1 enum Option<T> {
2 /// No value
3 None,
4 /// Some value `T`
5 Some(T),
6 }
Option used for optional values, partial functions, etc. No NULL!
1 enum Result<T, E> {
2 //! Contains the success value
3 Ok(T),
4 //! Contains the error value
5 Err(E),
6 }
Result used for error handling. No exceptions!
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42. Error Handling
1 let mut s = String::new();
2
3 match io::stdin().read_line(&mut s) {
4 Ok(_) => (),
5 Err(msg) =>
6 eprintln!("Cannot read line: {}", msg),
7 }
8
9 io::stdin().read_line(&mut s)
10 .expect("Panic: cannot read line!");
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43. Simplify error handling with try!
1 fn write_to_file_using_try() -> Result<(), io::Error> {
2 let mut file = try!(File::create("friends.txt"));
3 try!(file.write_all(b"JohnnMaryn"));
4 println!("I wrote to the file");
5 Ok(())
6 }
7 // This is equivalent to:
8 fn write_to_file_using_match() -> Result<(), io::Error> {
9 let mut file = match File::create("friends.txt") {
10 Ok(f) => f,
11 Err(e) => return Err(e),
12 };
13 match file.write_all(b"JohnnMaryn") {
14 Ok(x) => x,
15 Err(e) => return Err(e)
16 };
17 println!("I wrote to the file");
18 Ok(())
19 }
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44. Methods
1 struct Circle { radius: f64, center: Point<f64> }
2
3 impl Circle {
4 fn area(&self) -> f64 {
5 PI * (self.radius * self.radius)
6 }
7
8 fn perimeter(&self) -> f64 {
9 2.0 * PI * self.radius
10 }
11 }
12
13 fn main() {
14 let center = Point { x: 0.0, y: 0.0 };
15 let circle = Circle { radius: 2.0, center };
16 println!("circle.area() = {}", circle.area())
17 }
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45. Traits
1 pub trait Hash {
2 fn hash<H: Hasher>(&self, state: &mut H);
3 }
4 impl Hash for Circle {
5 fn hash<H: Hasher>(&self, state: &mut H) {
6 self.center.hash(state);
7 self.radius.hash(state);
8 }
9 }
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46. Traits
1 pub trait Hash {
2 fn hash<H: Hasher>(&self, state: &mut H);
3 }
4 impl Hash for Circle {
5 fn hash<H: Hasher>(&self, state: &mut H) {
6 self.center.hash(state);
7 self.radius.hash(state);
8 }
9 }
Some traits support automatic implementation!
1 #[derive(PartialEq, Eq, Hash)]
2 struct Circle { /* ... */ }
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47. Traits bounds
1 fn store<T: Hash>(x: T, warehouse: Warehouse<T>) {
2 // ... x.hash(state) ...
3 }
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48. Traits bounds
1 fn store<T: Hash>(x: T, warehouse: Warehouse<T>) {
2 // ... x.hash(state) ...
3 }
One can specify multiple bounds:
1 fn store<T>(x: T, warehouse: Warehouse<T>)
2 where T: Hash + Display {
3 // ... x.hash(state) ...
4 // ... println!("x = {}", x) ...
5 }
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49. Traits bounds
1 fn store<T: Hash>(x: T, warehouse: Warehouse<T>) {
2 // ... x.hash(state) ...
3 }
One can specify multiple bounds:
1 fn store<T>(x: T, warehouse: Warehouse<T>)
2 where T: Hash + Display {
3 // ... x.hash(state) ...
4 // ... println!("x = {}", x) ...
5 }
Monomorphisation applies, i.e. statically dispatched.
Dynamic dispatch is also available with trait objects.
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50. Default methods and inheritance
1 trait Valid {
2 fn is_valid(&self) -> bool;
3 fn is_invalid(&self) -> bool { !self.is_valid() };
4 }
Default implementation can be overridden.
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51. Default methods and inheritance
1 trait Valid {
2 fn is_valid(&self) -> bool;
3 fn is_invalid(&self) -> bool { !self.is_valid() };
4 }
Default implementation can be overridden.
Traits can inherit from other traits:
1 trait Eq : PartialEq {
2 // Addtional methods in Eq
3 }
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52. Allocating on the heap
By default, everything is stack-allocated:
Fast.
Scoped.
Limited in size.
Various explicit pointer types for heap-allocated data:
Box<T> for single ownership.
Rc<T> for shared ownership.
Arc<T> for shared, thread-safe ownership.
Cell<T> for interior mutability, i.e. through a &T.
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53. Undiscussed bits
Efficient and safe slices.
Hygienic macros.
unsafe code.
Interactions with C-ABI code.
Iterators: clean syntax, safe, efficient, e.g.
for x in xs {
process(x)
}
Closures.
Multi-threading.
Embedded rust.
The ecosystem: cargo and crates.io, rustup, tests, doc, . . .
Many, many more!
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54. Outline
1 Why?
2 What?
3 Discussion
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55. Questions and (possibly) answers
?And happy rusting!
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