Chapter 9. Structs

Long ago, when shepherds wanted to see if two herds of sheep were isomorphic, they would look for an explicit isomorphism.

John C. Baez and James Dolan, “Categorification”

Rust structs, sometimes called structures, resemble struct types in C and C++, classes in Python, and objects in JavaScript. A struct assembles several values of assorted types together into a single value, so you can deal with them as a unit. Given a struct, you can read and modify its individual components. And a struct can have methods associated with it that operate on its components.

Rust has three kinds of struct types, named-field, tuple-like, and unit-like, which differ in how you refer to their components: a named-field struct gives a name to each component, whereas a tuple-like struct identifies them by the order in which they appear. Unit-like structs have no components at all; these are not common, but more useful than you might think.

In this chapter, we’ll explain each kind in detail, and show what they look like in memory. We’ll cover how to add methods to them, how to define generic struct types that work with many different component types, and how to ask Rust to generate implementations of common handy traits for your structs.

Named-Field Structs

The definition of a named-field struct type looks like this:

/// A rectangle of eight-bit grayscale pixels.
struct GrayscaleMap {
    pixels: Vec<u8>,
    size: (usize, usize)
}

This declares a type GrayscaleMap with two fields named ...

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