Structs

Question 1

What is a struct?

Answer 1

A custom data type that lets you name and package together multiple related values that make up a meaningful group.

Question 2

What are the names and types of the pieces of data inside a struct?

Answer 2

fields

Question 3

How do you create an instance of a struct?

Answer 3

by specifying concrete values for each of the fields.

Question 4

How do you get a specific value from a struct?

Answer 4

Using dot notation

Question 5

Can certain fields in a struct be marked mutable?

Answer 5

No, the entire instance must be mutable.

Question 6

What type of syntax is used to specify a property and its value that have the same name, as in:
struct {
   name,
   email
}

Answer 6

field init shorthand syntax

Question 7

How do you create a new instance of a struct that uses most of the values of a previous instance?

Answer 7

Using struct update syntax:
let user2 = User {
  email: "someone@someplace.com",
  username: "johnsonw", 
  ...user1,
}

Question 8

What are tuple structs?

Answer 8

They have the added meaning the struct name provides but don’t have names associated with their fields. These are useful when you want to give the tuple a name such that it is different from other tuples.

struct Color(i32, i32, i32);
struct Point(i32, i32, i32);

Question 9

How do you access an element on a tuple or tuple struct?

Answer 9

By using a “.” followed by an index to access an individual value.

Question 10

What is a unit struct?

Answer 10

A struct that doesn’t have any fields

Question 11

When is a unit struct useful?

Answer 11

when you need to implement a trait on some type but don’t have any data that you want to store in the type itself

Question 12

Should structs own most of their data?

Answer 12

Generally, we want instances of a struct to own all of its data and for that data to be valid for as long as the entire struct is valid.

Question 13

Can data in a struct store a reference to data owned by something else?

Answer 13

Yes, but to do so requires the use of lifetimes.

Question 14

What does a lifetime guarantee for a struct?

Answer 14

Lifetimes ensure that the data referenced by a struct is valid for as long as the struct is.

Question 15

Should you prefer taking ownership of a struct or borrowing it?

Answer 15

You should prefer borrowing a struct.

Question 16

What trait does the “{}” tell println! to format with?

Answer 16

Display

Question 17

What is the Display trait intended for?

Answer 17

Direct end user consumption

Question 18

Why can’t structs be printed with the Display trait?

Answer 18

The way they should be printed is less clear because there are more display possibilities.

Question 19

Which trait do we use to print a struct?

Answer 19

Debug

Question 20

How do we use the debug trait when printing a struct?

Question 21

How do you include the Debug trait on a struct so that it can be printed?

Answer 21

Add the #[derive(Debug)] annotation just before the struct definition

Question 22

When using a large struct, it’s easier to read the output when it is formatted. How do we print a large struct in a way that is easier to read than when using {:?}?

Answer 22

Use {:#?}

Question 23

How are methods different from functions?

Answer 23

They are defined within the context of a struct, enum, or trait object and their first parameter is always “self”, which represents the instance of the struct the method is being called on.

Question 24

Where do you define a method?

Answer 24

Inside of an impl (implementation) block for the struct

Question 25

What are the three ways in which a method can take “self”?

Answer 25

1. It can take ownership
2. It can borrow self immutably
3. It can borrow self mutably

Question 26

If you just want to read data from the struct how should a method take “self”?

Answer 26

As an immutable reference

Question 27

If you want to read and write data on a struct how should a method take “self”?

Answer 27

As a mutable reference

Question 28

When would a method take ownership of “self”?

Answer 28

It’s rare. It usually is done when the method transforms self into something else and you want to prevent the caller from using the original instance after the transformation.

Question 29

What is the main benefit of using methods instead of functions?

Answer 29

organization

Question 30

Why doesn’t rust have the “->” operator like c++?

Answer 30

Rust uses a feature called automatic referencing and dereferencing.

Question 31

How does autmomatic referencing / defreferencing work?

Answer 31

When you call a method with object.something(), Rust automatically adds in &, &mut, or * so object matches the signature of the method.

Question 32

Why is automatic referencing / dereferencing allowed to work?

Answer 32

because methods have a clear receiver -> self

Question 33

What are associated functions?

Answer 33

Functions within impl blocks that don’t take self as a parameter.

Question 34

What are associated functions often used for?

Answer 34

creating constructors that will return a new instance of the struct

Question 35

How do you access an associated function?

Answer 35

StructName::associated_function_name()

Question 36

Can structs have multiple impl blocks?

Answer 36

Yes

Question 37

What do structs let you create?

Answer 37

custom types that are meaningful for your domain

Question 38

What do associated functions let you do?

Answer 38

namespace functionality that is particular to your struct without having an instance available