Rust Literals and Type Specification

Introduction

In this lab, we learn about literals in Rust and how to specify their types by adding a suffix. Suffixed literals have their types known at initialization, while unsuffixed literals' types depend on how they are used. The size_of_val function is used to determine the size of a variable in bytes, and it is called with its full path, std::mem::size_of_val. The size_of_val function is defined in the mem module, which is in turn defined in the std crate.

Note: If the lab does not specify a file name, you can use any file name you want. For example, you can use main.rs, compile and run it with rustc main.rs && ./main.

Literals

Numeric literals can be type annotated by adding the type as a suffix. As an example, to specify that the literal 42 should have the type i32, write 42i32.

The type of unsuffixed numeric literals will depend on how they are used. If no constraint exists, the compiler will use i32 for integers, and f64 for floating-point numbers.

fn main() {
    // Suffixed literals, their types are known at initialization
    let x = 1u8;
    let y = 2u32;
    let z = 3f32;

    // Unsuffixed literals, their types depend on how they are used
    let i = 1;
    let f = 1.0;

    // `size_of_val` returns the size of a variable in bytes
    println!("size of `x` in bytes: {}", std::mem::size_of_val(&x));
    println!("size of `y` in bytes: {}", std::mem::size_of_val(&y));
    println!("size of `z` in bytes: {}", std::mem::size_of_val(&z));
    println!("size of `i` in bytes: {}", std::mem::size_of_val(&i));
    println!("size of `f` in bytes: {}", std::mem::size_of_val(&f));
}

There are some concepts used in the previous code that haven't been explained yet, here's a brief explanation for the impatient readers:

• std::mem::size_of_val is a function, but called with its full path. Code can be split in logical units called modules. In this case, the size_of_val function is defined in the mem module, and the mem module is defined in the std crate. For more details, see modules and crates.

Summary

Congratulations! You have completed the Literals lab. You can practice more labs in LabEx to improve your skills.