3.7 KiB
Health Statistics
Welcome to Health Statistics on Exercism's Rust Track.
If you need help running the tests or submitting your code, check out HELP.md.
If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)
Introduction
It is often useful to group a collection of items together, and handle those groups as units. In Rust, we call such a group a struct, and each item one of the struct's fields. A struct defines the general set of fields available, but a particular example of a struct is called an instance.
Furthermore, structs can have methods defined on them, which have access to the fields. The struct itself in that case is referred to as self. When a method uses &mut self, the fields can be changed, or mutated. When a method uses &self, the fields cannot be changed: they are immutable. Controlling mutability helps the borrow-checker ensure that entire classes of concurrency bug just don't happen in Rust.
In this exercise, you'll be implementing two kinds of methods on a struct. The first are generally known as getters: they expose the struct's fields to the world, without letting anyone else mutate that value. In Rust, these methods idiomatically share the name of the field they expose, i.e., if we have a getter method that fetches a struct field called name, the method would simply be called name().
You'll also be implementing methods of another type, generally known as setters. These change the value of the field. Setters aren't very common in Rust--if a field can be freely modified, it is more common to just make it public--but they're useful if updating the field should have side effects, or for access control: a setter marked as pub(crate) allows other modules within the same crate to update a private field, which can't be affected by the outside world.
Structs come in three flavors: structs with named fields, tuple structs, and unit structs. For this concept exercise, we'll be exploring the first variant: structs with named fields.
Structs are defined using the struct keyword, followed by the capitalized name of the type the struct is describing:
struct Item {}
Additional types are then brought into the struct body as fields of the struct, each with their own type:
struct Item {
name: String,
weight: f32,
worth: u32,
}
Lastly, methods can be defined on structs inside of an impl block:
impl Item {
// initializes and returns a new instance of our Item struct
fn new() -> Self {
unimplemented!()
}
}
With that brief introduction to the syntax of structs out of the way, go ahead and take a look at the instructions for this exercise!
Instructions
You're working on implementing a health-monitoring system. As part of that, you need to keep track of users' health statistics.
You'll start with some stubbed functions in an impl block as well as the following struct definition:
pub struct User {
name: String,
age: u32,
weight: f32,
}
Your goal is to implement the stubbed out methods on the User struct defined in the impl block.
For example, the new method should return an instance of the User struct with the specified name, age, and weight values.
let mut bob = User::new(String::from("Bob"), 32, 155.2);
// Returns: a User with name "Bob", age 32, and weight 155.2
The weight method should return the weight of the User.
bob.weight();
// Returns: 155.2
The set_age method should set the age of the User.
bob.set_age(33);
// Updates Bob's age to 33; happy birthday Bob!
Have fun!