Rust

Getting Started with Rust: Working with Files and Doing File I/O

Mihalis Tsoukalos — Thu, 20 Jun 2019 11:30:00 +0000

How to develop command-line utilities in Rust.

This article demonstrates how to perform basic file and file I/O operations in Rust, and also introduces Rust's ownership concept and the Cargo tool. If you are seeing Rust code for the first time, this article should provide a pretty good idea of how Rust deals with files and file I/O, and if you've used Rust before, you still will appreciate the code examples in this article.

Ownership

It would be unfair to start talking about Rust without first discussing ownership. Ownership is the Rust way of the developer having control over the lifetime of a variable and the language in order to be safe. Ownership means that the passing of a variable also passes the ownership of the value to the new variable.

Another Rust feature related to ownership is borrowing. Borrowing is about taking control over a variable for a while and then returning that ownership of the variable back. Although borrowing allows you to have multiple references to a variable, only one reference can be mutable at any given time.

Instead of continuing to talk theoretically about ownership and borrowing, let's look at a code example called ownership.rs:


fn main() {
    // Part 1
    let integer = 321;
    let mut _my_integer = integer;
    println!("integer is {}", integer);
    println!("_my_integer is {}", _my_integer);
    _my_integer = 124;
    println!("_my_integer is {}", _my_integer);

    // Part 2
    let a_vector = vec![1, 2, 3, 4, 5];
    let ref _a_correct_vector = a_vector;
    println!("_a_correct_vector is {:?}", _a_correct_vector);

    // Part 3
    let mut a_var = 3.14;
    {
        let b_var = &mut a_var;
        *b_var = 3.14159;
    }
    println!("a_var is now {}", a_var);
}

So, what's happening here? In the first part, you define an integer variable (integer) and create a mutable variable based on integer. Rust performs a full copy for primitive data types because they are cheaper, so in this case, the integer and _my_integer variables are independent from each other.

However, for other types, such as a vector, you aren't allowed to change a variable after you have assigned it to another variable. Additionally, you should use a reference for the _a_correct_vector variable of Part 2 in the above example, because Rust won't make a copy of a_vector.

Go to Full Article

Text Processing in Rust

Mihalis Tsoukalos — Mon, 18 Mar 2019 13:07:07 +0000

by Mihalis Tsoukalos

Create handy command-line utilities in Rust.

This article is about text processing in Rust, but it also contains a quick introduction to pattern matching, which can be very handy when working with text.

Strings are a huge subject in Rust, which can be easily realized by the fact that Rust has two data types for representing strings as well as support for macros for formatting strings. However, all of this also proves how powerful Rust is in string and text processing.

Apart from covering some theoretical topics, this article shows how to develop some handy yet easy-to-implement command-line utilities that let you work with plain-text files. If you have the time, it'd be great to experiment with the Rust code presented here, and maybe develop your own utilities.

Rust and Text

Rust supports two data types for working with strings: String and str. The String type is for working with mutable strings that belong to you, and it has length and a capacity property. On the other hand, the str type is for working with immutable strings that you want to pass around. You most likely will see an str variable be used as &str. Put simply, an str variable is accessed as a reference to some UTF-8 data. An str variable is usually called a "string slice" or, even simpler, a "slice". Due to its nature, you can't add and remove any data from an existing str variable. Moreover, if you try to call the capacity() function on an &str variable, you'll get an error message similar to the following:


error[E0599]: no method named `capacity` found for type
 ↪`&str` in the current scope

Generally speaking, you'll want to use an str when you want to pass a string as a function parameter or when you want to have a read-only version of a string, and then use a String variable when you want to have a mutable string that you want to own.

The good thing is that a function that accepts &str parameters can also accept String parameters. (You'll see such an example in the basicOps.rs program presented later in this article.) Additionally, Rust supports the char type, which is for representing single Unicode characters, as well as string literals, which are strings that begin and end with double quotes.

Finally, Rust supports what is called a byte string. You can define a new byte string as follows:

Go to Full Article

Linux Journal October 2018: Programming

Carlie Fairchild — Mon, 01 Oct 2018 14:59:55 +0000

by Carlie Fairchild

Welcome to the Programming issue, October 2018, of Linux Journal. This month we highlight programming languages new and old including Go, Rust, Clojure and Bash. Take a look at this month's complete line-up:

Featured articles in this issue include:

Understanding Bash: Elements of Programming** This article is available online now as a sneak peak in to our October issue.
Getting Started with Rust: Working with Files and Doing File I/O
Introductory Go Programming Tutorial
Creating Linux Command-Line Tools in Clojure

Additional articles:

Shall We Study Amazon's Pricing Together?
Review: System76 Oryx Pro Laptop
3D-Printed Firearms Are Blowing Up
FOSS Project Spotlight: Tutanota, the First Encrypted Email Service with an App on F-Droid
Introducing Genius, the Advanced Scientific Calculator for Linux

Columns:

Kyle Rankin's Hack and /: Papa's Got a Brand New NAS: the Software
Shawn Powers' The Open-Source Classroom: Have a Plan for Netplan
Reuven M. Lerner's At the Forge: Automate Sysadmin Tasks with Python's os.walk Function
Dave Taylor's Work the Shell: Normalizing Filenames and Data with Bash
Zack Brown's diff -u: What's New in Kernel Development
Glyn Moody's Open Sauce: Now Is the Time to Start Planning for the Post-Android World

Subscribers, you can download your October issue now.

Not a subscriber? It’s not too late. Subscribe today and receive instant access to this and ALL back issues since 1994!

Want to buy a single issue? Buy the August magazine or other single back issues in the LJ store.

Go to Full Article