Generics Types, Traits, and Lifetimes

Question 1

What are generics?

Answer 1

Abstract stand-ins for concrete types or other properties.

Question 2

When defining a function that uses generics, where do we place the generic in the signature?

Answer 2

Where the parameter data types and return values are,

Question 3

What are placed between <> in function signatures between the function name and the parameter list when using generics in a function?

Answer 3

Type name declarations.

Question 4

What is an example of a function signature with generics?

Answer 4

fn largest(list: &[T]) -> T {}

Question 5

What is an example of using generics in a struct definition?

Answer 5

struct Point {
x: T,
y: U,
}

Question 6

What is an example of using generics with an enum definition?

Answer 6

enum Result {
Ok(T),
Err(E),
}

Question 7

How does Rust avoid performance cost when using generics?

Answer 7

By using monomorphization.

Question 8

What is monomorphization?

Answer 8

The process of turning generic code into specific code by filling in the concrete types that are used when compiled.

Question 9

What do traits do?

Answer 9

Tell the Rust compiler about functionality a particular type has and can share with other types.

Question 10

What are trait definitions?

Answer 10

A way to group method signatures together to define a set of behaviors necessary to accomplish some purpose.

Question 11

What is the syntax for implementing a trait on a type?

Answer 11

impl  for  {
    fn foo(&self) ->  {
       ...
    }
}

Question 12

How do you use a default trait function on a type?

Answer 12

Specify an empty impl block . impl for {}

Question 13

Provide an example of how to define a function that accepts many different types.

Answer 13

pub fn notify(item: impl Summary) {
println!(“Breaking news! {}”, item.summarize());
}

Question 14

What is the impl trait syntactic sugar for?

Answer 14

trait bounds.

Question 15

Where are trait bounds placed in a function signature?

Answer 15

With the declaration of the generic type parameter after a colon and inside angle brackets.

Question 16

How can you force multiple generic parameters to have the same type?

Answer 16

Using trait bounds.

Question 17

How can you specify more than one trait bound?

Answer 17

Using the + syntax. e.g.
pub fn notify(item: impl Summary + Display) {
or
pub fn notify(item: T) {

Question 18

Whats an example of using the where clause with trait bounds?

Answer 18

fn some_function(t: T, u: U) -> i32
where T: Display + Clone,
U: Clone + Debug
{

Question 19

Whats an example of a return type that implements a trait in a function?

Answer 19

fn returns_summarizable() -> impl Summary {
Tweet {
username: String::from(“horse_ebooks”),
content: String::from(“hello world”)
}
}

Question 20

When a function implements a trait on a return type, how many types can you return?

Answer 20

exactly one.