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My_Learning-Rust

Rust 🦀 programming language learning.

Cheatsheet

Mindmap:

Rust

Installation

For Linux or macOS

Including VMs

Compiler

Following tools get installed: rustup, rustc, cargo, rustfmt

Different release channels

  • stable: stable, but has a 6-week stabilization period
  • beta: unstable, but has a 6-week stabilization period
  • nightly: unstable, but has the latest features

rustup is for managing different rust toolchain versions for different targets/architectures (arm, x86, etc.)

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

info: downloading installer

Welcome to Rust!

This will download and install the official compiler for the Rust
programming language, and its package manager, Cargo.

Rustup metadata and toolchains will be installed into the Rustup
home directory, located at:

  /Users/abhi3700/.rustup

This can be modified with the RUSTUP_HOME environment variable.

The Cargo home directory is located at:

  /Users/abhi3700/.cargo

This can be modified with the CARGO_HOME environment variable.

The cargo, rustc, rustup and other commands will be added to
Cargo's bin directory, located at:

  /Users/abhi3700/.cargo/bin

This path will then be added to your PATH environment variable by
modifying the profile files located at:

  /Users/abhi3700/.profile
  /Users/abhi3700/.bash_profile
  /Users/abhi3700/.bashrc
  /Users/abhi3700/.zshenv

You can uninstall at any time with rustup self uninstall and
these changes will be reverted.

Current installation options:


   default host triple: aarch64-apple-darwin
     default toolchain: stable (default)
               profile: default
  modify PATH variable: yes

1) Proceed with installation (default)
2) Customize installation
3) Cancel installation

Editor

Use VSCode.

Extensions:

Source

The list might get updated over the time. Refer to your VSCode extension list.

An ideal setup for a rust code (with tests) would be:

So, here on left terminal, we have $ cargo watch -x run running, which will watch for changes in the project and automatically run. On right terminal, we have $ cargo watch -x test running, which will watch for changes in the project and automatically test.

Commands

rustup

  • set stable as default toolchain via $ rustup default stable

  • set nightly as default toolchain via $ rustup default nightly

  • set nightly as default toolchain for a specific project via $ rustup override set nightly

    If any repository has rust-toolchain.toml file present, then the toolchain version mentioned in the file will be used for that project if you have already switched to that toolchain.

  • All the rust binaries are installed in this folder $HOME/.cargo/bin

  • Update all channels using $ rustup update [RECOMMENDED]

    stable-aarch64-apple-darwin updated - rustc 1.72.1 (d5c2e9c34 2023-09-13) (from rustc 1.72.0 (5680fa18f 2023-08-23))
beta-aarch64-apple-darwin updated - rustc 1.74.0-beta.1 (b5c050feb 2023-10-03) (from rustc 1.73.0-beta.3 (bc28abf92 2023-08-27))
nightly-aarch64-apple-darwin updated - rustc 1.75.0-nightly (187b8131d 2023-10-03) (from rustc 1.74.0-nightly (84a9f4c6e 2023-08-29))
    • And then need to set the latest rustc & cargo for individual channels: stable, beta, nightly
      • $ rustup default stable-aarch64-apple-darwin
      • $ rustup default beta-aarch64-apple-darwin
      • $ rustup default nightly-aarch64-apple-darwin

  • Update the toolchain (of stable channel): $ rustup update stable

  • Update all toolchains (irrespective of channel): $ rustup update

  • View installed version via $ rustup show

  • Check if there is any latest version using $ rustup check

  • install a specific version via $ rustup install 1.64.0 or $ rustup install 1.64.0-aarch64-apple-darwin

  • set a specific version in the already set channel via $ rustup default 1.64.0 or $ rustup override set 1.64.0

  • Uninstall rustup using $ rustup self uninstall

  • toolchains:

    • List all installed toolchains using $ rustup toolchain list
    • Install a toolchain using $ rustup toolchain install <toolchain-name-w-version-arch-developer>. E.g. $ rustup toolchain install 1.70.0-aarch64-apple-darwin
    • Uninstall a toolchain using $ rustup toolchain uninstall <toolchain-name-w-version-arch-developer>. E.g. $ rustup toolchain uninstall 1.70.0-aarch64-apple-darwin

  • lib:

    • Show all available lib using $ rustup component list
    • Show all installed lib using $ rustup component list --installed
    • Install rust std lib using $ rustup component add rust-src

  • target (for a toolchain):

    • Show all available target using $ rustup target list
    • show all installed target using $ rustup target list --installed
    • Install rust target using $ rustup target add <component-name>. E.g. $ rustup target add wasm32-unknown-unknown

      Here, unknown means that it is for any OS.

  • Some components to be installed

    • clippy: $ rustup component add clippy
    • rustfmt: $ rustup component add rustfmt
    • rust-src: $ rustup component add rust-src
    • docs: $ rustup component add rust-docs

cargo

new

  • $ cargo new <package-folder-name>: Create a new project with folder & package named as given.
    • $ cargo new hello: Create a project folder named 'hello' & the package name as hello in Cargo.toml file.
  • $ cargo new <folder-name> --name <package-name>: Create a new project with folder name different than the package name.
    • $ cargo new demo --name game-demo: Here, demo is the folder name whereas the package name is game-demo in Cargo.toml file.

add

  • $ cargo add <package-name>: add package to [dependencies] locally into the rust project. E.g. $ cargo add dotenv.
  • $ cargo add <package-name> --dev: add package to [dev-dependencies] locally into the rust project. E.g. $ cargo add hex-literal --dev.

install

  • $ cargo install --list: list globally installed packages via .

  • $ cargo install --path <path/to/folder/containing/Cargo.toml>: install the binaries in by default /target/release (by default) folder . This will install the binary in the ~/.cargo/bin folder. In case of workspace, parse the path of the bin folder containing Cargo.toml file.

    • After this, if you want to uninstall the binary, then you can do it via $ cargo uninstall <bin-name>. Suppose, you installed a binary named hello via $ cargo install --path <path/to/folder/containing/Cargo.toml>, then you can uninstall it via $ cargo uninstall hello.

  • Install a git repo using cargo: $ cargo install --git https://github.com/dimensionhq/fleet fleet-rs. And then use fleet like this:

    fleet -h

  • Install cargo-edit: for helping with edit, add, remove, upgrade, downgrade, and list dependencies in Cargo.toml

  • Install cargo-watch: via $ cargo install cargo-watch.

    • Watch for changes in the project and automatically run via $ cargo watch -x run
    • Watch for changes in the project and automatically test via $ cargo watch -x test

  • cargo-expand: install via $ cargo install cargo-expand. more here

  • cargo-audit: install via $ cargo install cargo-audit.

doc

  • cargo doc --open: Open doc of project. Used when it's not a workspace.
  • cargo doc --package <PACKAGE_NAME> --open: Open doc of package in a workspace

update

  • $ cargo update: This command will update dependencies in the Cargo.lock file to the latest version. If the Cargo.lock file does not exist, it will be created with the latest available versions.

build, check

  • $ cargo +nightly build: build using nightly toolchain for a project

  • $ cargo build: build a debug version of a project using set toolchain (view via $ rustup show).

  • $ cargo build --release: build a release (optimized) version of a project

    Often, cargo check is much faster than cargo build, because it skips the step of producing an executable. If you’re continually checking your work while writing the code, using cargo check will speed up the process! As such, many Rustaceans run cargo check periodically as they write their program to make sure it compiles or they depend on rust-analyzer (sometimes not accurate as exprienced in big blockchain codebase like substrate where target/ folder is 25 GB+) Then they run cargo build when they’re ready to use the executable.

test

  • $ cargo test: run all the tests in a project & also captures the output by default. That means output from println! won't be shown when run.

  • $ cargo test -- --nocapture: run all the tests in a project by keeping the output (i.e. println! statements) hidden. That means output from println! would not be shown when run by default as tests are not meant for it, rather to check assert.. statements. But, using this flag -- --nocapture, the output is shown.

  • $ cargo test <module-name>::<test-function-name> run a specific test function in a module. E.g. $ cargo test tests::test_add_two_and_two for rust code:

    #[cfg(test)]
mod tests {
    #[test]
    fn test_add_two_and_two() {
        assert_eq!(4, add_two_and_two());
    }

    fn add_two_and_two() -> i32 {
        4
    }
}
    • if there is a single or a few test function(s) then it is better to use #[test] attribute. But, if there are many test functions, then it is better to use #[cfg(test)] attribute to put into module.

  • View the dependency graph of a project using $ cargo tree

publish

  • Publish a crate to crates.io via $ cargo publish

    • Each crate has a limit of 10 MB in size for each version.
    • $ cargo publish --dry-run won't upload, just check if everything is fine.
    • $ cargo publish will upload the crate to crates.io
    • crates can't be deleted, but can be yanked i.e. a particular version can be removed from crates.io
      • $ cargo yank --version 1.0.1 will yank the version 1.0.1 from crates.io
      • $ cargo yank --version 1.0.1 --undo will undo the yank
    • cargo owner can add/remove owner (individual or team)
    cargo owner --add github-handle
cargo owner --remove github-handle
cargo owner --add github:rust-lang:owners
cargo owner --remove github:rust-lang:owners

workspace

  • Add workspace member(s) to manage multiple projects inside one rust project (containing Cargo.toml file):

    • $ mkdir hello
    • $ cd hello
    • $ touch Cargo.toml
    • Add this to Cargo.toml file:
    [workspace]
members = ["project1", "project2", "project3"]
resolver = "2"

    Here, resolver is added to ensure that all the members/projects follow rust 2021 or else, set to "1".

    • $ cargo new project1
    • $ cargo new project2
    • $ cargo new project3
    • $ cargo build: Build the workspace

    Now, you would also view the linting in all repos.

  • Make Binary inside lib: Any file (with main function) inside a cargo lib project can be defined as binary for easy call via target/release/<bin>

    For instance, inside a cargo project, the project folder looks like this:

    folder structure: 
    └── src
  ├── accumulator.rs
  ├── bn_solidity_utils.rs
  ├── client
  │   └── main.rs
  ├── constants.rs
  ├── contracts
  │   ├── Semacaulk.json
  │   ├── Verifier.json
  │   ├── format
  │   ├── foundry.toml
  │   ├── lib
  │   ├── mod.rs
  │   ├── script
  │   ├── sol
  │   └── tests
  ├── demo
  │   └── main.rs
  ├── error.rs
  ├── gates
  │   ├── gate_sanity_checks.rs
  │   ├── mod.rs
  │   ├── tests.rs
  │   └── utils.rs
  ├── keccak_tree
  │   └── mod.rs
  ├── kzg.rs
  ├── layouter
  │   └── mod.rs
  ├── lib.rs
  ├── mimc7.rs
  ├── multiopen
  │   ├── mod.rs
  │   ├── prover.rs
  │   └── verifier.rs
  ├── prover
  │   ├── mod.rs
  │   ├── precomputed.rs
  │   ├── prover.rs
  │   └── structs.rs
  ├── rng.rs
  ├── setup
  │   ├── main.rs
  │   ├── mod.rs
  │   └── tests.rs
  ├── tests
  │   ├── mod.rs
  │   └── prover_and_verifier.rs
  ├── transcript.rs
  ├── utils.rs
  └── verifier
      └── mod.rs

    Now, inside the main Cargo.toml file, all the required binary could be added like this:

    [[bin]]
edition = "2021"
name = "setup"
path = "src/setup/main.rs"

[[bin]]
edition = "2021"
name = "demo"
path = "src/demo/main.rs"

[[bin]]
edition = "2021"
name = "client"
path = "src/client/main.rs"

    Now, you can call /target/release/client to call the client program.

    Repo as reference.

NOTE: If there is any error related to linker with C, follow this:

You will also need a linker, which is a program that Rust uses to join its compiled outputs into one file. It is likely you already have one. If you get linker errors, you should install a C compiler, which will typically include a linker. A C compiler is also useful because some common Rust packages depend on C code and will need a C compiler.

On macOS, you can get a C compiler by running:

xcode-select --install

CI/CD (Github Actions)

Create a .github/workflows/rust-ci.yml file.

The file should contain this:

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Set up Rust
        uses: actions/checkout@v2
      - name: Install cargo-audit
        run: cargo install cargo-audit
      - name: Build
        run: cargo build --verbose
      - name: Test
        run: cargo test --verbose
      - name: Clippy
        run: cargo clippy --verbose -- -D warnings
      - name: Audit
        run: cargo audit

Crates

Important ones.

For more, see here.

Repositories

C++ vs Rust

Getting Started

Code

fn main() {
    println!("Hello World!");
}

Build

cargo can also be used for compiling a project like node in NodeJS project.

rustc hello.rs
cargo build

Output

./hello

Practice

Put the code inside a .rs file & link into ./tuts/src/main.rs using #[path= "path/to/file"] macro.

Concepts

“Ownership is Rust’s most unique feature, and it enables Rust to make memory safety guarantees without needing a garbage collector.”

  • By default, all the variables are defined as immutable equivalent to const in JS/TS.
  • In Rust, borrowing is analogous to referencing in C++ & dereferencing is same as that of C++.
  • The value of mutable variable can be changed, but not the type.
  • In Rust, every value has a single owner that determines its lifetime.
  • Rust has preferred composition over inheritance. That's why in Rust, we use traits to define shared behavior.

Primitive types and Variables

  1. Various sizes of integers, signed and unsigned (i32, u8, etc.)
  2. Floating point types f32 and f64.
  3. Booleans (bool)
  4. Characters (char). Note these can represent unicode scalar values (i.e. beyond ASCII)

usize: the size is dependent on the kind of computer your program is running on: 32 bits if you’re on a 32-bit architecture and 64 bits if you’re on a 64-bit architecture.

str vs String

str String
Primitive Type Built-in struct
Doesn’t have ownership of the string as it is typically used by reference Has ownership of the string
It is a string slice It is a growable array
Size known at compile time Size is unknown at compile time
Data allocated in the data segment of the application binary Data allocated in a heap
Uses & or reference to assign a str value to a variable Not need need to use & or reference to assign a String value to a variable

  • &str to String is always an expensive operation, as it is owned with a String type.

    let name: &str = "Abhijit Roy"
let name_String: String = name.to_string(); // used `to_string()` to convert from `&str` to `String` type

  • String to &str is a cheap operation, as it is borrowed with a &str type.

    let name: String = "Abhijit Roy"
let name_String: &str = &name; // used `&` to convert from `String` to `&str` type

  • The following function is more expensive than the latter.

    fn main() {
    let my_str: &str = "This is a str";

    // converting the str to String is an expensive operation
    print_data(&my_str.to_string());

    print!("printing inside main {}", my_str);
}

fn  print_data(data: &String) {
    println!("printing my data {} ", data);
}
    fn main() {
    let my_string: String = String::from("Understanding the String concept?");

    print_data(&my_string);

    print!("printing inside main {}", my_string);
}

fn  print_data(data: &str) {
    println!("printing my data {} ", data);
}

    Source

Print

    1. formatting variables inside println function
let name = "Abhijit";
let age = 28;

println!("My name is {name}, and age is {age}");        // ❌
println!("My name is {0}, and age is {1}", name, age);  // ✔️
println!("My name is {}, and age is {}", name, age);    // ✔️
    1. Multiple usage of variables without repetition
let alice = "Alice";
let bob = "Bob";

println!("{0}, this is {1}. {1}, this is {0}", alice, bob);

Attributes

Here, each aforementioned cases like unused variables, dead code, means something (shown on hover) like this:

This means "allow unused imports". Hence, the compiler will not show any warning for unused variable.

This means "not to allow detecting dead code". Hence, the compiler will not show warning for dead code.

As code example, see this:

//! This won't show any warning for unused import.

#[allow(unused_imports)]
use std::io::{self, Write};

Pointer

  • Box<T> - A pointer type for heap allocation

    By default, in Rust variables are stored in stack. But, if we want to store in heap, we can use Box<T> pointer. This is similar to new keyword in JS/TS.

  • Box is basically used for:

    • For dynamic allocation of memory for variables.
    • When there is a lot of data that we need to transfer ownership and we don’t want that they are copied.

Mutex

Mutex stands for Mutual Exclusion, and it's a synchronization primitive used to protect shared data in concurrent programming. In the context of Rust, the std::sync::Mutex type provides a mechanism for multiple threads to mutually exclude each other from accessing some particular data.

Let's imagine we have a book 📚 (representing the shared data), and we have two friends 👥 (representing two threads). They both want to write in the book 📚 at the same time.

The book 📚 is our shared data that both friends 👥 want to modify. We can't have both friends 👥 writing in the book 📚 at the same time, because that would create a mess. We need some way to ensure that only one friend 👥 can write in the book 📚 at a time. That's where our Mutex comes in!

A mutex is like a key 🔑 to the book 📚. When a friend 👥 has the key 🔑, they can write in the book 📚. When they're done, they give the key 🔑 back, and the other friend 👥 can take the key 🔑 to write in the book 📚.

Here is how it works in code:

use std::sync::Mutex;

let m = Mutex::new(5);  // Here we are creating our book 📚 with a number 5 inside it.

{
    let mut num = m.lock().unwrap();  // One of our friends 👥 takes the key 🔑.
    *num = 6;  // They change the number in the book 📚 from 5 to 6.
}  // The friend 👥 gives back the key 🔑 when they are done.

println!("m = {:?}", m);  // Now the book 📚 has number 6 inside it.

In this example, the friend 👥 is able to take the key 🔑 (acquire the lock) by calling m.lock(). They can then modify the data (write in the book 📚) by dereferencing num to get access to the data. When they're done, they give the key 🔑 back automatically because Rust's scoping rules will drop the MutexGuard (represented by num) at the end of the scope, which releases the lock.

It's important to remember that if a friend 👥 forgets to give back the key 🔑 (doesn't release the lock), the other friend 👥 will be left waiting indefinitely, unable to write in the book 📚. This is called a deadlock, and it's a common problem in concurrent programming that you should try to avoid.

This is a simplified view of mutexes in Rust, but hopefully, it helps you understand the basic concept. For more complex scenarios, you'll want to learn about things like error handling with Result, using Condvar for condition variables, and understanding the different methods available on Mutex and MutexGuard.

Memory: stack, heap

  • Stack (fixed size like char, bool, int, array; less costly; quick to access by calling var like easy to copy the var)

  • Heap (variable size like string, vector, class; more costly; access var or object via pointer)

  • The memory of the declared variables are dropped (or freed) when the program leaves a block in which the variable is declared.
    • E.g. Normally, inside the main function, whenever a variable is defined, it is dropped after exiting the main function.
fn main() {
    // Case-1
    let x = 10;
    let r = &x;

    let k;
    {
        let y = Box::new(5);            // Using Box pointer for storing into heap
        let y = 5;              // stored in stack
        // let y <'a> = 5;
        // k = &y;         // y dropped here as it is not available for lifetime. Moreover the block is getting over after this
        k = y;          // this implies that the ownership of 5 is transferred to `k` from `y`
    }
}

Casting

Collection

Conditional

Function

Borrowing & Ownership

Lifetimes

Error handling

Modules

Struct

Trait

Generics

Macros

Concurrency(./tuts/concurrency/README.md)

Comments

Here are some of the key guidelines for writing comments in Rust:

  • Use /// for documenting items such as functions, structs, enums, and modules. The comment should describe what the item does, its parameters (if any), and its return value (if any).
  • Use //! for documenting the crate root. This comment should provide a brief overview of the crate's purpose and functionality.
  • Use // for adding comments to individual lines of code. These comments should explain what the code is doing and why it's necessary.
  • Use Markdown formatting to add emphasis, headings, lists, and links to your comments.
  • Keep your comments concise and to the point. Avoid unnecessary details or redundant information.
  • Use proper spelling, grammar, and punctuation in your comments.
  • Update your comments when you make changes to your code. Outdated comments can be misleading and confusing.

super vs crate

This is important while importing modules.

  • super is used to import from parent module of the current module (file). When you use super for importing, you're specifying a relative path from the current module's parent.

    // Assuming we have a module hierarchy like this:
// my_module
// ├── sub_module1
// │   ├── sub_module1_1
// │   │   ├── some_file.rs
// │   ├── MyStruct.rs
// ├── sub_module2

// In some_file.rs
use super::MyStruct;

  • crate is used to import from root module of the current module (file). When you use crate for importing, you're specifying an absolute path from the root of the current crate (where Cargo.toml file is there).

    // Assuming we have a module named `my_module` at the root of our crate
use crate::my_module::MyStruct;

lib or bin

  • $ cargo init --lib <name> creates a lib
  • $ cargo init <name> creates a package

Move | Copy | Clone

Testing

All tests like unit, integration tests are in tests folder.

  • add panic in test to fail the test

      #[test]
  #[should_panic]
  fn fail_creating_weightless_package() {
      let sender_country = String::from("Spain");
      let recipient_country = String::from("Austria");

      Package::new(sender_country, recipient_country, -2210);
  }

  • add #[ignore] to skip the test.

Miscellaneous

Picked from this book: Rust Design Patterns

Look for files with _opt suffix like this at the repo root:

❯ find . | grep _opt

Clippy

Use this tool to get the code related issues (if any).

Simple way to install:

rustup component add clippy

Run this to get the issues:

cargo clippy

Understanding memory layout (low level language design)

Video source 🌟🌟🌟🌟🌟

  • stack is used for:

    • primitive types
    • function param, return values (address), local variables

  • For 64-bit machine, total allowed stack size for the main thread is 8 MB. In below example, there are different stack frame created. Consider the entire white area as stack size for main thread as 8 MB. Also, there is only 1 thread running. Here, stack pointer is getting incremented/decremented based on the program logic running in the thread.

    Here, the blurred one is not deallocated, but just be replaced by the next function.

Idioms

Use Borrowed types for arguments

&String -> &str
&Vec<T> -> &[T]
&Box<T> -> &T

Code

Reference

Concatenate strings with format

format!("{} World!", s1)

Code

Reference

Use collect wherever possible to create a collection

let s = "Abhijit is a good boy"; // collection of bytes like
// [65, 98, 104, 105, 106, 105, 116, 32, 105, 115, 32, 97, 32, 103, 111, 111, 100, 32, 98, 111, 121]
let v = s.bytes().collect::<Vec<u8>>(); // RECOMMENDED for iteration

Code

Reference

Some macros implicitly always borrow. So, not need to use & explicitly

let x = 5;
println!("x = {}", x);

Reference

Coherence (Overlap) and Orphan Rules

  • Coherence/Overlap rule: There should not be multiple implementations using impl for the same type.
  • Orphan rule: The trait or type should be defined in the same crate as the implementation.

✅

// crate_a
struct MyStruct;

trait MyTrait {
    fn my_fn(&self);
}

❌

// crate_b
use crate_a::{MyStruct, MyTrait};

// WRONG: Orphan rule violation
impl MyTrait for MyStruct {
    fn my_fn(&self) {
        println!("Hello");
    }
}

This would be illegal under the orphan rules, because both MyType and MyTrait are foreign to Crate B. If this were allowed, and Crate A also provided an implementation of MyTrait for MyType, there would be a conflict, and Rust wouldn't know which implementation to use. The orphan rules prevent this situation from arising.

Tools

  • Check behind-the-code for a code snippet - https://play.rust-lang.org/
    • Tools >> Expand Macros
  • Debugger tool

    • FireDBG

      git clone https://github.com/SeaQL/FireDBG.for.Rust.git
cd FireDBG.for.Rust
cargo install --path ./command

Fields

Application Development

  • Best 2:
    1. Rocket (good docs) [Familiar]
    2. Actix_web (under development) [Recommended]

      2 is much faster than 1 in terms of performance. Infact, it is closer to drogon-core (in C++)

Blockchain

AI | ML | DL

Embedded Systems

Data Science

Troubleshoot

1. warning: path statement with no effect

  • Cause: there is a statement having no effect
  • Solution: Assign the variable to _.

Before:

    let result = match grade {
        "A" => { println!("Excellent!"); },
        "B" => { println!("Great!"); },
        "C" => { println!("Good"); },
        "D" => { println!("You passed"); },
        "F" => { println!("Sorry, you failed"); },
        _ => { println!("Unknown Grade"); }
    };

    result;

After:

    let result = match grade {
        "A" => { println!("Excellent!"); },
        "B" => { println!("Great!"); },
        "C" => { println!("Good"); },
        "D" => { println!("You passed"); },
        "F" => { println!("Sorry, you failed"); },
        _ => { println!("Unknown Grade"); }
    };

    // result;             // warning: path statement with no effect, Solution --> assign to `_`
    let _ = result;

2. warning: variant is never constructed, error[E0277]: UsState doesn't implement Debug

  • Cause: It simply means that the variant is never used, "constructed", anywhere in your program. There is no AppAction::Task anywhere in the program. Rust expects that if you say an enum variant exists, you will use it for something somewhere.
  • Solution: by putting this before the enum, or individually before intentionally unused items, you can make the warning disappear:

Before:

enum UsState {
 California,
 Mexico,
 Alaska,
}

enum Coin {
 Penny,
 Nickel,
 Dime,
 Quarter,
 Custom(UsState),
}

After:

#[allow(dead_code)]
#[derive(Debug)]  // this use is recommended, otherwise there is error.
enum UsState {
 California,
 Mexico,
 Alaska,
}

#[allow(dead_code)]
enum Coin {
 Penny,
 Nickel,
 Dime,
 Quarter,
 Custom(UsState),
}

3. Error: "move occurs...which does not implement the Copy trait"

  • Cause: Copy designates types for which making a bitwise copy creates a valid instance without invalidating the original instance.

This isn't true for String, because String contains a pointer to the string data on the heap and assumes it has unique ownership of that data. When you drop a String, it deallocates the data on the heap. If you had made a bitwise copy of a String, then both instances would try to deallocate the same memory block, which is undefined behaviour.

  • Solution: Just use format like this:

Before:

impl Detail for Car {
    fn brand(&self) -> String {
        return self.brand;
    }
    fn color(&self) -> String {
        return self.color;
    }
}

After:

impl Detail for Car {
    fn brand(&self) -> String {
        // using `format` instead of directly returning the brand bcoz it throws error:
        // "move occurs because `self.brand` has type `String`, which does not implement the `Copy` trait"
        return format!("{}", self.brand);
    }
    fn color(&self) -> String {
        return format!("{}", self.color);
    }
}

4. Error: mismatched types expected i32, found usize

Cause: Because of type mismatch

Solution: Just typecast it as the required type

res.push(i as i32);

5. error: the 'cargo' binary, normally provided by the 'cargo' component, is not applicable to the '1.70.0-aarch64-apple-darwin' toolchain

  • Cause: It happens on a particular rust codebase. In my case, it happened with aptos-core repo.
  • Solution: Just remove & then add cargo via this: Source
1. rustup component remove cargo
2. rustup component add cargo

6. Error: Blocking waiting for file lock on the registry index

  • Cause: The index is locked by another process. This mainly happens when $ cargo run is executed after opening a rust project in VS Code while $ cargo check is being run by rust-analyzer extension. Try to run any command after rust-analyzer is completed.
  • Solution: If after long wait, it doesn't go away, then just delete few files:
rm -rf ~/.cargo/registry/index/* ~/.cargo/.package-cache
cargo clean

And then run the command $ cargo build/$ cargo check/$ cargo run again. It would work fine now 🎉.

7. Error: error[E0635]: unknown feature stdsimd

  • Cause: This is a common issue when trying to update the channel to latest nightly version. This is because the Cargo.lock file uses 2 versions of ahash which conflicts. This can be confirmed by running $ cargo tree -i ahash.

  • Solution: Just follow the steps below:

    1. Remove your Cargo.lock file or you can just remove either of the versions (preferably older).
    2. [OPTIONAL] Clean the target/ folder using $ cargo clean.
    3. Build again $ cargo build.

8. Don't install rust using homebrew brew on macOS

  • Cause: It might happen that if you install some package using brew like maturin (a project management tool in Python) uses rust. They essentially install/override rust with that of homebrew. You can verify if your rustc is being called by rust binary of brew like this:
$ which rustc
/opt/homebrew/bin/rustc

You might find these errors when compiling rust project:

error[E0554]: `#![feature]` may not be used on the stable release channel
...
  • Solution: Just remove/uninstall rust from brew (if found in $ brew list | grep rust). Secondly, remove the package that are dependents like maturin (in my case). Next, check $ which rustc.
where rustc
/opt/homebrew/bin/rustc
/opt/homebrew/bin/rustc
/opt/homebrew/bin/rustc
/Users/abhi3700/.cargo/bin/rustc

Delete /opt/homebrew/bin/rustc via $ rm -rf /opt/homebrew/bin/rustc. Now, check it should be called by that of .cargo binary instead of brew.

$ which rustc
/Users/abhi3700/.cargo/bin/rustc

Now, cargo clean >> cargo build should work fine in rust project.

Fixed 🎉.

Quiz

There is a section called quiz in this repo. It contains some questions and their solutions. The plan is to add them into Rustlings later in an organized manner.

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