Learning Rust

By Paul Johnson , Vesa Kaihlavirta
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    Introducing and Installing Rust
About this book
Rust is a highly concurrent and high performance language that focuses on safety and speed, memory management, and writing clean code. It also guarantees thread safety, and its aim is to improve the performance of existing applications. Its potential is shown by the fact that it has been backed by Mozilla to solve the critical problem of concurrency. Learning Rust will teach you to build concurrent, fast, and robust applications. From learning the basic syntax to writing complex functions, this book will is your one stop guide to get up to speed with the fundamentals of Rust programming. We will cover the essentials of the language, including variables, procedures, output, compiling, installing, and memory handling. You will learn how to write object-oriented code, work with generics, conduct pattern matching, and build macros. You will get to know how to communicate with users and other services, as well as getting to grips with generics, scoping, and more advanced conditions. You will also discover how to extend the compilation unit in Rust. By the end of this book, you will be able to create a complex application in Rust to move forward with.
Publication date:
November 2017


Chapter 1. Introducing and Installing Rust

Rust is a fairly new addition to the ever-growing number of programming languages available to developers. If you've never used Rust, but come from pretty much any procedural language (such as C or Pascal) or are used to shell scripting, then you should very quickly feel right at home when using Rust.

Getting to grips with Rust is simple enough, and in this chapter we will cover the following topics:

  • Installing Rust with rustup
  • Testing the installation
  • Setting up a project
  • Looking at the IDEs available
  • Automation using Cargo

Installing Rust

As with most languages, Rust is available for a wide number of platforms. It would be impossible to go through installing the compiler on every variant of every operating system. Fortunately, there's an official method of installing Rust, and even though the details may differ slightly, the process is almost the same on all platforms. Therefore, this book will cover installing Rust using rustup on Fedora 27.

https://rustup.rs always contains up-to-date instructions on how to get going on all platforms. On Linux and macOS, it will look something like this:

On Windows, this text is replaced by a link to rustup-init.exe, which is an executable that installs and sets up rustup on Windows.

Installing rustup on Linux

Run the suggested command that is shown at https://rustup.rs. Run this command in a Terminal. The script suggests some defaults and asks you to confirm them. This is roughly what it should look like after completing the whole script:

Note that this script attempts to set up rustup for your user by editing your .profile and .bash_profile files. If you are using a custom setup, such as another shell, you may need to add the source $HOME/.cargo/env command manually.

After finishing this script, you can verify that it worked by logging off and on from your Terminal and verifying that the tools are in your path:

gcc prerequisites

To build any software that links against external libraries, you will need a C compiler and development versions of any libraries you may be linking against. To ensure that things work properly, install the compiler using the standard method for your operating system.

In Fedora, this would be done using the dnf tool:

sudo dnf install -y gcc

If you are unsure whether you have gcc installed, type the following command in a terminal window:

gcc -version

If gcc is installed, you'll see something like this:

Testing your installation

Open a command-prompt window and type this:

rustc --version

If everything was installed correctly, you will see something like this:

Integrated Development Environment

To effectively code Rust, you will need at least some sort of text editor. All popular editors are properly supported, so if your favorite is Vim, Emacs, or any of the others, you will find a high-quality Rust extension there. The website https://areweideyet.com/ should give a current view of how things are.

We will cover the lightweight IDE from Microsoft, Visual Studio Code, and its most current Rust extension, called simply Rust. This IDE should work fairly well in all the different desktop environments. Installation instructions and packages for several platforms are available at Visual Studio Code's main site, https://code.visualstudio.com.

  1. Open up Visual Studio Code and go to the Command Palette, either by the View menu or by the keyboard shortcut Ctrl + Shift + P (which may differ between platforms). Type in install extension to look for the proper command, and then select Install Extensions:
  1. After selecting this, type rust into the next field to look for the Rust extension. At the time of writing, the most recent one is made by kalitaalexey:
  1. You can install Rust right away by pressing Install; alternatively, click on the list item itself to show information about the extension first. After installing it, reload the editor. The Rust extension is now installed and ready to use!

Your first Rust project

Your first Rust project is not going to be particularly amazing. If anything, it's going to serve four purposes:

  • Showing the structure of a Rust project
  • Showing how to create a project by hand
  • Showing how to create a project using the Rust Cargo script
  • Compiling and executing the program

Structure of a Rust project

A Rust project (irrespective of the platform you are developing on) will have the following structure:

The preceding screenshot shows the structure of the simplest Rust project, and as such can be replicated using the following commands:

OS X/Linux

Windows (from the command prompt)

mkdir firstproject cd firstproject touch Cargo.toml mkdir src cd src touch main.rs
md firstproject cd firstproject md src echo $null >> Cargo.toml cd src echo $null >> main.rs


The echo $null >> filename command creates an empty file without the need to start Notepad; save the file and exit.

The Cargo.toml file is the Rust equivalent of a Makefile. When the .toml file is created by hand, it should be edited to contain something like this:

The structure of a Rust project can expand to include documentation as well as the build structure, as follows:

Automating things

While there is nothing wrong with creating a Rust project by hand, Rust does come with a very handy utility called Cargo. Cargo can be used not only to automate the setting up of a project, but also to compile and execute Rust code. Cargo can be used to create the parts required for a library instead of an executable, and can also generate application documentation.

Creating a binary package using Cargo

As with any other script, Cargo works (by default) on the current working directory. (For example, while writing this chapter, my working directory for the example code is ~/Developer/Rust/chapter0 on the Mac and Linux boxes, and J:\Developer\Rust\Chapter0 on the Windows 10 machine.)

In its simplest form, Cargo can generate the correct file structure like this:

cargo new demo_app_name -bin

The preceding command tells Cargo to create a new structure called demo_app_name, and that it is to be a binary. If you remove -bin, it creates a structure called, which is going to be a library (or more accurately, something other than a binary).

If you don't wish to use the root (say you want to create a library within your binary framework), then instead of demo_app_name, you append the structure before the name relating to your working directory.

In the small example I gave earlier, if I wanted to create a library within my binary structure, I would use the following:

cargo new app_name/mylib

That will create a structure like this:

The Cargo.toml file requires no editing (at this stage), as it contains the information we had to enter manually when we created the project by hand.


Cargo has a number of directory separator translators. This means that the preceding example can be used on OS X, Linux, and Windows without an issue; Cargo has converted the / to \ for Windows.

Using Cargo to build and run an application

As we are all able to create directory structures, Cargo is then able to build and execute our source code.

If you look at the source code that comes with this chapter, you will find a directory called app_name. To build this package using Cargo, type the following from a Terminal (or command on Windows) window:

cd app_name cargo build app_name

This will build the source code; finally you will be informed that the compilation has been successful:

Next, we can use Cargo to execute the binary as follows:

cargo run

If everything has worked, you will see something like the following:

As with any sort of utility, it's possible to "daisy-chain" the build and execution into one line, as follows:

cargo build; cargo run


You may be wondering why the first operation performed was to move into the application structure rather than just type cargo build. This is because Cargo is looking for the Cargo.toml file (remember, this acts as a build script).

Cleaning your source tree with Cargo

When the Rust compiler compiles the source files, it generates something known as an object file. The object file takes the source file (which we can read and understand) and compiles this into a form that can be joined with other libraries to create a binary.

This is a good idea, as it cuts down on compilation time; if a source file has not been changed, there is no need to recompile the file, as the object file will be the same.

Sometimes, the object file becomes out of date, or code in another object file causes a panic due to conflicts. In this case, it is not uncommon to "clean" the build. This removes the object files, and the compiler then has to recompile all the source files.

Also, it should always be performed prior to creating a release build.

The standard Unix make program performs this with the clean command (make clean). Cargo performs the clean operation in a way similar to the make utility in Unix:

cargo clean

A comparison of the directories shows what happens when using the preceding Cargo command:

The entire target directory structure has simply been removed (the preceding screenshot was from a Mac, hence the dSYM and plist files. These do not exist on Linux and Windows).

Creating documentation using Cargo

As with other languages, Rust is able to create documentation based on meta tags with the source files. Take the following example:

fn main() 
   print_multiply(4, 5); 
/// A simple function example 
/// # Examples 
/// ``` 
/// print_multiply(3, 5); 
/// ``` 
fn print_multiply(x: i32, y: i32) 
   println!("x * y = {}", x * y); 

The comments preceded by /// will be converted into documentation.

The documentation can be created in one of two ways: via Cargo or by using the rustdoc program.

rustdoc versus Cargo

As with the other operations provided by Cargo, when documentation is created, it acts as a wrapper for rustdoc. The only difference is that with rustdoc you have to specify the directory that the source file sits in. Cargo acts dumb in this case, and creates the documentation for all source files.

In its simplest form, the rustdoc command is used as follows:

cargo docrustdoc src/main.rs

Cargo does have the advantage of creating the doc structure within the root folder, whereas rustdoc creates the structure within the target (which is removed with cargo clean).

Using Cargo to help with your unit testing

Hopefully, unit testing is not something you will be unfamiliar with. A unit test is a test that operates on a specific function or method rather than an entire class or namespace. It ensures that the function operates correctly on the data it is presented with.

Unit tests within Rust are very simple to create (two examples are given in the assert_unittest and unittest directories). The following has been taken from the unittest example:

fn main() { 
    println!("Tests have not been compiled, use rustc --test instead (or cargo test)"); 
fn multiply_test() 
   if 2 * 3 == 5 
      println!("The multiply worked"); 

When this is built and executed, you may be surprised by the following result:


The reason why this unit test has passed despite 2 x 3 not being 5 is because the unit test is not testing the result of the operation, but that the operation itself is working. It is very important that this distinction is understood from an early stage to prevent confusion later.

We have hit a limitation of unit testing: if we are not testing the data but the operation, how can we know that the result itself is correct?

Assert yourself!

Unit testing provides the developer with a number of methods called assertion methods:

fn multiply() 
   assert_eq!(5, 2 * 3); 

In the preceding code snippet, we use the assert_eq! (assert equal) macro. The first argument is the answer expected, and the second argument is what is being tested. If 2 * 3 = 5, then the assertion is true and passes the unit test.

Is there anything Cargo can't do?

For a Rust developer, Cargo is an amazing utility. In addition to these common facilities, it also has other commands, which are listed in the table that follows. All commands follow this form:

cargo <command> <opts>


What it does


This command fetches the dependencies of a package from the network. If a lockfile is available, this command will ensure that all of the Git dependencies and/or registry dependencies are downloaded and locally available. The network is never called after a cargo fetch unless the lockfile changes.

If the lockfile is not available, then this is the equivalent of cargo generate-lockfile. A lockfile is generated and all the dependencies are also updated.


This command generates the lockfile for a project. The lockfile is typically generated when cargo build is issued (you will see it as Cargo.lockfile in the directory structure).


This command checks out a Git repository. You will need to use it in the following form:

cargo git-checkout -url=URL

This command locates a package.


This command saves an API token from the registry locally. The call is in the following form:

cargo login -host=HOST   token

This command manages the owners of a crate on the registry. This allows the ownership of a crate (a crate is a Rust library) to be altered (--add LOGIN or -remove LOGIN) as well as adding tokens to the crate.

This command will modify the owners for a package on the specified registry (or the default). Note that the owners of a package can upload new versions, yank old versions, and also modify the set of owners, so be cautious!


This command assembles the local package into a distributable tarball.


This command prints a fully qualified package specification.


This command uploads a package to the registry.


This command reads the manifest file (.toml).


This command compiles the complete package.

The specified target for the current package will be compiled along with all of its dependencies. The specified options will all be passed to the final compiler invocation, not any of the dependencies. Note that the compiler will still unconditionally receive arguments such as -L, --extern, and --crate-type, and the specified options will simply be added to the compiler invocation.

This command requires that only one target is being compiled. If more than one target is available for the current package, the filters --lib, --bin, and so on—must be used to select which target is compiled.


This command searches for packages at https://crates.io/.


This command updates dependencies as recorded in the local lockfile.

Typical options are:

  • --package SPEC (package to update)
  • --aggressive (forcibly update all dependencies of <name> as well)
  • --precise PRECISE (update a single dependency to exactly PRECISE)

This command requires that a Cargo.lock file already exists as generated by cargo build or related commands.

If a package spec name (SPEC) is given, then a conservative update of the lockfile will be performed. This means that only the dependency specified by SPEC will be updated. Its transitive dependencies will be updated only if SPEC cannot be updated without updating the dependencies. All other dependencies will remain locked at their currently recorded versions.

If PRECISE is specified, then --aggressive must not also be specified. The argument PRECISE is a string representing a precise revision that the package being updated should be updated to. For example, if the package comes from a Git repository, then PRECISE would be the exact revision that the repository should be updated to.

If SPEC is not given, then all the dependencies will be re-resolved and updated.


This command ensures that the project is correctly created.


This command shows the version of Cargo.


This command removes a pushed crate from the index.

The yank command removes a previously pushed crate version from the server's index. This command does not delete any data, and the crate will still be available for download via the registry's download link.

Note that existing crates locked to a yanked version will still be able to download the yanked version to use it. Cargo will, however, not allow any new crates to be locked to any yanked version.


As you can now appreciate, the Cargo utility script is extremely powerful and flexible.



We now have a fully working installation of Rust, and are ready for the get-go. We've explained how to set up a project, both manually and via the Cargo utility, and you should already have an appreciation of how useful Cargo is.

In the next chapter, we'll be looking at the foundation of any language: variables.

About the Authors
  • Paul Johnson

    Paul Johnson has been writing software since the early 1980s on machines ranging from the ZX81 and servers to his trusty Mac, and has used more languages than he can remember. He is a qualified scuba diver and college lecturer. Paul lives with his wife, kids, and pets, and listens to an inordinate amount of rock and metal on Primordial Radio. This is his third book for Packt.

    Browse publications by this author
  • Vesa Kaihlavirta

    Vesa Kaihlavirta has been programming since he was five, beginning with C64 Basic. His main professional goal in life is to increase awareness of programming languages and software quality in all industries that use software. He's an Arch Linux Developer Fellow, and has been working in the telecom and financial industry for a decade. Vesa lives in Jyvaskyla, central Finland.

    Browse publications by this author
Latest Reviews (2 reviews total)
The book is not bad, but definitely not good either. Begginers would be totally lost and would not understand half of the things, or frustrated. So, if you are begginer, I don't recommend at all. If you are slightly into rust, you can take it. Also some C++ knowledge would be a big plus while reading this book.
see my previous remark, I don't want to rate every book seperately
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