Book Image

Rust Essentials - Second Edition

By : Ivo Balbaert
Book Image

Rust Essentials - Second Edition

By: Ivo Balbaert

Overview of this book

Rust is the new, open source, fast, and safe systems programming language for the 21st century, developed at Mozilla Research, and with a steadily growing community. It was created to solve the dilemma between high-level, slow code with minimal control over the system, and low-level, fast code with maximum system control. It is no longer necessary to learn C/C++ to develop resource intensive and low-level systems applications. This book will give you a head start to solve systems programming and application tasks with Rust. We start off with an argumentation of Rust's unique place in today's landscape of programming languages. You'll install Rust and learn how to work with its package manager Cargo. The various concepts are introduced step by step: variables, types, functions, and control structures to lay the groundwork. Then we explore more structured data such as strings, arrays, and enums, and you’ll see how pattern matching works. Throughout all this, we stress the unique ways of reasoning that the Rust compiler uses to produce safe code. Next we look at Rust's specific way of error handling, and the overall importance of traits in Rust code. The pillar of memory safety is treated in depth as we explore the various pointer kinds. Next, you’ll see how macros can simplify code generation, and how to compose bigger projects with modules and crates. Finally, you’ll discover how we can write safe concurrent code in Rust and interface with C programs, get a view of the Rust ecosystem, and explore the use of the standard library.
Table of Contents (13 chapters)

Using trait constraints


Back in the section on Generic data structures and functions in Chapter 5, Higher Order Functions and Error-Handling, we made a function sqroot to calculate the square root of a 32-bit floating point number:

// see code in Chapter 5/code/sqrt_match.rs 
Use std::f32; 
 
fn sqroot(r: f32) -> Result<f32, String> { 
if r < 0.0 {  
return Err("Number cannot be negative!".to_string());  
} 
   Ok(f32::sqrt(r)) 
} 

What if we wanted to calculate the square root of an f64 type number? It would be very unpractical to make a different version of the function for each type. A first attempt would be to just replace an f32 type with a generic type <T>:

// see code in Chapter 6/code/trait_constraints.rsfn sqroot<T>(r: T) -> Result<T, String> { 
   if r < 0.0 {  
      return Err("Number cannot be negative!".to_string());  
   } 
    Ok(T::sqrt(r)) 
} 

But Rust does not agree because it doesn't know anything about T, signaling multiple errors:

   ...