Enums and Pattern Matching

Question 1

What is enum short for?

Answer 1

Enumerations.

Question 2

What do enums allow for?

Answer 2

Define a type by enumerating its possible values.

Question 3

What is the keyword used to create an enum?

Answer 3

enum.

Question 4

What do we call the possible values of an enum?

Answer 4

The variants.

Question 5

How are variants of an enum namespaced?

Answer 5

Under their identifier. syntax: idntifier::variant;

Question 6

How do we attach data to an enum variant?

Answer 6

Comma separated list of each data type inside parentheses or an anonymous struct.

Question 7

How do we define methods for enums

Answer 7

impl enum_name {
    fn foo(&self)...
}

Question 8

What is the Option enum?

Answer 8

Enum defined by the standard library that encodes a common scenario in which a value could be something or it could be nothing.

Question 9

What does Rust have in place of nulls?

Answer 9

The enum Option

Question 10

How is Option defined in the standard library?

Answer 10

enum Option {
Some(T),
None,
}

Question 11

What does it mean when we have a Some value?

Answer 11

That a value is present and the value is held within the Some.

Question 12

What does it mean when we have a None value?

Answer 12

The is no valid value.

Question 13

Why is Option better than null?

Answer 13

Because Option and T (where T can be any type) are different types. Any value of Type T is guaranteed to be not null. If a value is of Option, the null case MUST be explicitly handled.

Question 14

What does the match control flow operator allow for?

Answer 14

Comparing a value against a series of patterns and then executing code based on which pattern matches. Also match arms can bind to the parts of the values that match the pattern.

Question 15

What does it mean that Matches are exhaustive in Rust?

Answer 15

All possibilities of the match must be handled for the code to compile.

Question 16

What will _ match in match operation?

Answer 16

All cases that are not specified before it.

Question 17

What does the if let control flow allow for?

Answer 17

A less verbose way to handle values that match one pattern while ignoring the rest.

Question 18

What does an if let statement do?

Answer 18

if let permits patterns matching within the condition of an if statement. … If a pattern matches successfully, it binds any appropriate parts of the value to the identifiers in the pattern, then evaluates the expression. If the pattern doesn’t match, nothing happens.

Question 19

What is an example of an if let statement?

Answer 19

if let Some(3) = some_u8_value {
println!(“three”);
}