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What is an enum in Rust?

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In Rust, an enum is a data structure that declares its different subtypes. An enum enables the same functionality as a struct, but it does so with less code. For example, implementing different types of Machine, where each machine has a different set of attributes, requires a different struct for each machine. On the other hand, we can incorporate all of these different types of machines into a single enum:

struct Phone {}
struct Adder {
x: i,
y: i,
}
struct Computer {
name: String,
}

Additionally, creating a function that can take any type of Machine as its parameter is not possible using structs; in such a case, enums must be used. With an enum, the type of machine can be identified inside the function by using pattern matching with the match keyword.

#![allow(unused_variables)]
fn main() {
#[allow(dead_code)]
enum Machine {
Phone,
Adder(i8, i8),
Computer(String),
}
// A function taking any Machine as parameter:
fn foo(m: Machine) {
match m {
Machine::Phone => println!("This is a phone"),
Machine::Adder(a, b) => println!("Sum: {}", a + b),
Machine::Computer(name) => println!("Name: {}", name),
}
}
let machine_1 = Machine::Phone;
let machine_2 = Machine::Adder(3, 4);
let machine_3 = Machine::Computer("Mainframe".to_string());
foo(machine_1);
foo(machine_2);
foo(machine_3);
}

A function can also be declared for an enum using the impl keyword, which is similar to a struct:

#![allow(unused_variables)]
fn main() {
#[allow(dead_code)]
enum Machine {
Phone,
Adder(i8, i8),
Computer(String),
}
impl Machine{
fn foo(&self) {
match self {
Machine::Phone => println!("This is a phone"),
Machine::Adder(a, b) => println!("Sum: {}", a + b),
Machine::Computer(name) => println!("Name: {}", name),
}
}
}
let machine_1 = Machine::Phone;
let machine_2 = Machine::Adder(3, 4);
let machine_3 = Machine::Computer("Mainframe".to_string());
machine_1.foo();
machine_2.foo();
machine_3.foo();
}

RELATED TAGS

rust
struct
enum
data structure
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