README

A place to sharpen skills in case they get rusty.

We follow the good book 'ere

Notes

Cargo

• Cargo new creates a standard directory structure and a git repo
• Cargo build builds a binary - it'll land in the target/debug directory
• Cargo build --release builds a binary for release - it takes longer but adds optimizations
• Cargo run builds and runs the binary
• Cargo check verifies that the binary compiles

Assorted

• expect() will panic with a custom message
• match will let us handle the error instead

Shadowing

Variables can be shadowed - i.e declare the same variable multiple times, with different values (even different types!). However you cannot shadow a mut variable with a different type. The variables are scoped.

fn main() {
    let x = 5;

    let x = x + 1;

    {
        let x = x * 2;
        println!("The value of x in the inner scope is: {12}", x);
    }

    println!("The value of x is: {6}", x);

    let x = "banana"


    println!("The value of x is: {banana}", x);
}

Tuples

Tuples have a fixed length and can contain multiple types.

let t: (i32, f64, u8) = (500, 2.4, 8);

# Tuple values can be accessed by index
let five_hundred = x.0; 

# Tuples can also be deconstructed
let five_hundred, two_point_four, eight = t; 

Arrays

Arrays have a fixed length and can only contain a single type. Arrays are allocated on the stack rather than the heap. A vector is like an array except it can grow/shrink in size.

# You can declare the type and size of the array using type hinting inside
# square brackets
 let a:[i32: 3] = [4, 100, 10];

# You can fill an array using value; size syntax as follows
let a = [3; 5];
# This is equivalent to 
let a = [3, 3, 3, 3, 3];

You can allocate vectors using the builtin vec!() macro.

    // creates a vector [0, 1]
    let mut fib: Vec<u32> = vec![0, 1];

Statements and Expressions

Statements are instructions that perform some action and do not return a value. Expressions evaluate to a resulting value. Let’s look at some examples.

let y = 6; # Expression

    let y = { # Everything inside the {} is an expression.. so expressions can be part of statements. Consider that let y = 4 is a statement!
        let x = 3;
        x + 1 # This line does not have a semicolon as it is an expression. If it did it would not return a value! 
    };

Structs

You can build functions whose parameters match struct fields to avoid using the field: value syntax.

# Declaring a struct
struct User {
    active: bool,
    username: String,
    email: String,
    sign_in_count: u64,
}

# Declaring a struct method
# self is short for self: Self where Self is a type alias for User inside the impl block
# Methods can take ownership so self can be owned, borrowed or mutably borrowed. 
impl User {
    fn isActive(&self) -> bool {
        self.active
    }
}

# A bit like in Go Rust will automatically de/reference an object when you call
a method on it. That means the below statements are synonymous
p1.distance(&p2);
(&p1).distance(&p2);

# Associated functions are functions that are associated with a certain type but are not Methods
impl User {
    fn active_user() -> User {
        User {
            active: true
        }
    }
}

# They are typically used as constructors and are accessed using `::` syntax
let active_user = User::active_user();

# Declaring a tuple struct, which is essentially just a named tuple but they are different types.
struct Color(i32,i32,i32);
struct Black(i32,i32,i32);

fn build_user(email: String, username: String) -> User {
    User {
        email,
        username,
        active: true,
        sign_in_count: 1,
    }
}

# Create structs from other structs and override only specific fields. 
# This is known as the update syntax
let user2 = User {
        email: String::from("[email protected]"),
        ..user1
};

The reason for specifying user2 = User... above is that we are actually moving the values from user1 -> user2. We will no longer be able to access user1 after the data is moved.

Unless...

Remember that types that implement the Copy trait can be copied as they are types with known sizes at compile time so they live on the stack. If the User struct only had fields with types that implemented Copy then we could still access user1 after the copy.

Enums

struct Ipv4Addr {
    // --snip--
}

struct Ipv6Addr {
    // --snip--
}

# Enums can embed structs
enum IpAddr {
    V4(Ipv4Addr),
    V6(Ipv6Addr),
}

Packages, Crates and Modules

A package is one or more crates. The Cargo.toml file contained by a package defines how to build those crates.

Crates are composed of modules. Crates come in two flavours; binary and library

• Binary crates are programs that compile to an executable that is run.
• Library crates are don't have a main function and don't compile to an executable. Instead they provide shareable functionality.

A package can contain many binary crates, but only a single library crate. A package can have multiple binary crates by placing files in the src/bin directory: each file will be a separate binary crate.