Named Structs

Like C and C++, Rust has support for custom structs:

# // Copyright 2023 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
struct Person {
    name: String,
    age: u8,
}

fn describe(person: &Person) {
    println!("{} is {} years old", person.name, person.age);
}

fn main() {
    let mut peter = Person {
        name: String::from("Peter"),
        age: 27,
    };
    describe(&peter);

    peter.age = 28;
    describe(&peter);

    let name = String::from("Avery");
    let age = 39;
    let avery = Person { name, age };
    describe(&avery);
}

Key Points:

• Structs work like in C or C++.
  • Like in C++, and unlike in C, no typedef is needed to define a type.
  • Unlike in C++, there is no inheritance between structs.
• This may be a good time to let people know there are different types of structs.
  • Zero-sized structs (e.g. struct Foo;) might be used when implementing a trait on some type but don’t have any data that you want to store in the value itself.
  • The next slide will introduce Tuple structs, used when the field names are not important.
• If you already have variables with the right names, then you can create the struct using a shorthand.
• Struct fields do not support default values. Default values are specified by implementing the Default trait which we will cover later.

More to Explore

• You can also demonstrate the struct update syntax here:

  rust,ignoreCopy

  # // Copyright 2023 Google LLC
  # // SPDX-License-Identifier: Apache-2.0
  #
  let jackie = Person { name: String::from("Jackie"), ..avery };
  

• It allows us to copy the majority of the fields from the old struct without having to explicitly type it all out. It must always be the last element.

• It is mainly used in combination with the Default trait. We will talk about struct update syntax in more detail on the slide on the Default trait, so we don't need to talk about it here unless students ask about it.