Rust Structures Creating and using structure values


Consider the following struct definitions:

struct Foo {
    my_bool: bool,
    my_num: isize,
    my_string: String,
struct Bar (bool, isize, String);
struct Baz;

Constructing new structure values for these types is straightforward:

let foo = Foo { my_bool: true, my_num: 42, my_string: String::from("hello") };
let bar = Bar(true, 42, String::from("hello"));
let baz = Baz;

Access fields of a struct using .:

assert_eq!(foo.my_bool, true);
assert_eq!(bar.0, true); // tuple structs act like tuples

A mutable binding to a struct can have its fields mutated:

let mut foo = foo;
foo.my_bool = false;
let mut bar = bar;
bar.0 = false;

Rust's pattern-matching capabilities can also be used to peek inside a struct:

// creates bindings mb, mn, ms with values of corresponding fields in foo
let Foo { my_bool: mb, my_num: mn, my_string: ms } = foo;
assert_eq!(mn, 42);
// .. allows you to skip fields you do not care about
let Foo { my_num: mn, .. } = foo;
assert_eq!(mn, 42);
// leave out `: variable` to bind a variable by its field name
let Foo { my_num, .. } = foo;
assert_eq!(my_num, 42);

Or make a struct using a second struct as a "template" with Rust's update syntax:

let foo2 = Foo { my_string: String::from("world"), .. foo };
assert_eq!(foo2.my_num, 42);