Rust

General

• Default integer type: i32

• Ownership

  • Each resource can have only one owner at a time.
  • References are variables which can access data without owning it.

• Destructuring: Looks like pattern matching

  • https://doc.rust-lang.org/rust-by-example/flow_control/match/destructuring/destructure_tuple.html

• References

  • &: shared reference
  • &mut: mutable reference

• Lifetime: Prefixed with an apostrophe.

  • Eg: 'static.
  • https://doc.rust-lang.org/nomicon/lifetimes.html

• Box<T>: simplest form of heap allocation

  • Provides ownership of allocated memory

• Names ending with ! are macros

  • Eg: println!, ~

• &[i32]: a 'slice'. A 'pointer' to an array (also contains info about the length of the array)

• Panic: like an error ???

• unsafe { }: code which won't be typechecked by compiler for type safety ??

• '{:?} formats the "next" value passed to a formatting macro, and supports anything that implements Debug.'

  • https://stackoverflow.com/questions/38157335/what-does-mean-in-a-rust-format-string

• Raw borrow: &raw const ??

• Value expressions vs place expressions

  • A subtle difference ?
  • Place expression: like lvalue in C
  • Value expression: like rvalue in C
  • https://www.ralfj.de/blog/2024/08/14/places.html

Debug trait

Useful for printing values helpful for the programmer.

#[derive(Debug)]
enum List<T>{
    Nil,
    Cons(T, Box<List<T>>),
}

Misc

• TUI libraries: cursive, ratatui, crossterm

References

https://doc.rust-lang.org/rust-by-example/flow_control/match/destructuring/destructure_pointers.html

• Syntax is similar to pointers in C.
• Create a reference to x: &x
• Dereference a reference rf: *rf

Printing

See:

• https://doc.rust-lang.org/std/fmt/
• https://doc.rust-lang.org/rust-by-example/hello/print.html

Formatting traits:

Copy semantics

• All stack allocated values have copy semantics.
• Types with copy semantics have Copy traits.
  • Copy and Clone traits are similar but have different purposes.
  • https://doc.rust-lang.org/std/marker/trait.Copy.html#whats-the-difference-between-copy-and-clone

Move semantics

https://doc.rust-lang.org/rust-by-example/scope/move.html

• Types with copy semantics have Drop trait (to drop ownership)
  • To prevent accidental use, Drop::drop() can't be called manually.
  • https://doc.rust-lang.org/std/ops/trait.Drop.html#you-cannot-call-dropdrop-yourself

Example: Box

Box has move semantics by default.

This works:

fn foo () {
  let x = Box::new(5);
  println!("x is: {}", x);
}

fn main() {
  foo();
}
/*
$ rustc hello.rs && ./hello
x is: 5
*/

This works too:

fn foo (x: Box<i32>) {
  println!("x is: {}", x);
}

fn main() {
  let x = Box::new(5);
  foo(x);
  //println!("x is: {}", x);
}

But this doesn't:

fn foo (x: Box<i32>) {
  println!("x is: {}", x);
}

fn main() {
  let x = Box::new(5);

  // ownership of x 'moves' to foo. main no longer owns x
  foo(x);

  // main is trying to use something it doesn't own. Error!
  println!("x is: {}", x);
}

Error is:

error[E0382]: borrow of moved value: `x`
 --> hello.rs:9:24
  |
7 |   let x = Box::new(5);
  |       - move occurs because `x` has type `Box<i32>`, which does not implement the `Copy` trait
8 |   foo(x);
  |       - value moved here
9 |   println!("x is: {}", x);
  |                        ^ value borrowed here after move
  |
note: consider changing this parameter type in function `foo` to borrow instead if owning the value isn't necessary
 --> hello.rs:2:12
  |
2 | fn foo (x: Box<i32>) {
  |    ---     ^^^^^^^^ this parameter takes ownership of the value
  |    |
  |    in this function
  = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider cloning the value if the performance cost is acceptable
  |
8 |   foo(x.clone());
  |        ++++++++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0382`.

cargo

http://web.mit.edu/rust-lang_v1.25/arch/amd64_ubuntu1404/share/doc/rust/html/cargo/guide/creating-a-new-project.html

# --bin for binary program (--lib for library)
# initializes a git repo by default. Disabling with --vcs none
cargo new <proj_name>  --bin --vcs none

# Or
cargo new <proj_name>  --lib --vcs none

cargo build