Defining a Class in Rust in Rust

Full lesson:

So far, you've worked with built-in types like i32, &str, and arrays. But what if you want to model something the language doesn't have a type for — like a Dog, a BankAccount, or a Game?

That's what structs are for. A struct lets you define your own type by listing what data it holds and what actions it can perform.

Why structs?

Imagine you're writing a program about dogs. Each dog has a name, an age, and can bark. Without structs, you'd have to track each dog's name in one variable, age in another, and write a separate bark() function for each. That gets messy fast.

With a struct, you bundle all of that into one neat package called Dog:

struct Dog {
    // We'll add fields and methods in upcoming lessons.
}

The syntax

Defining an empty struct in Rust looks like this:

struct StructName {
}

Three things to notice:

• The keyword struct tells Rust you're defining a new type.

• StructName is the name you choose. By convention, Rust struct names use PascalCase — capitalized words with no underscores: Dog, BankAccount, HighScore.

• The curly braces { } hold the body of the struct. Unlike C++, Rust does not require a semicolon after the closing brace when the struct has a body.

No classes: struct + impl:

Rust has no classes. You put the data in a struct, and its methods in a separate impl block. Methods take &self; functions without self are associated functions, called as Type::func().

struct Dog {
    name: String,
}

impl Dog {
    fn new(name: String) -> Dog {   // associated function: Dog::new(...)
        Dog { name }
    }
    fn bark(&self) {                // method: takes &self
        println!("{} says woof!", self.name);
    }
}

Your task

Define an empty struct called Dog. The pre-filled code in mainFunction will create an instance of your struct and print a confirmation message. If you define the struct correctly, the program will compile and print:

Defined the Dog class!