Fundamentals

Question 1

Name the rules of ownership.

Answer 1

1. Each value has a variable called its owner.
2. There can only be one owner at a time.
3. When an owner goes out of scope the value will be dropped

Question 2

List all built-in copy types.

Answer 2

• booleans
• all integers
• all floats
• tuples of copy types

Question 3

List the rules of references.

Answer 3

1. At any given time, you can have either but not both of:
   
   • One mutable reference
   • Any number of immutable references
2. References must always be valid

Question 4

List all available enum variants.

Answer 4

• unit like (no arguments)
• tuple like (positional arguments)
• struct like (named arguments)

Question 5

List the module rules.

Answer 5

1. If module foo has no submodules put its definitions in a file named foo.rs
2. If foo has submodules put its definitions in foo/mod.rs

Question 6

List the privacy rules.

Answer 6

1. pub items can be accessed by any parent module.
2. everything else can only be accessed by their immediate parent module and all child modules.

Question 7

Types allowing shared ownership.

Answer 7

• std::rc::RC / std::rc::Weak
• std::sync::Arc

Question 8

How do Rc/Weak and Arc work?

Answer 8

• By implementing the Clone, Drop and Deref traits
  
  1. .clone() increments reference count
  2. .drop() decrements reference count
  3. other method calls are delegated to their contained value
  4. their own functionality is implemented as associated functions

Question 9

Name two types that all enable interior mutability.

Answer 9

Cell & RefCell

Question 10

How can you access a copy of the value contained in a Cell?

Answer 10

fn get(&self) -> T

with T: Copy

Question 11

How can you change the value contained in a Cell?

Answer 11

fn set(&self, val: T)

with T: Copy

Question 12

What is the difference between a Cell and a RefCell?

Answer 12

Cell does not let you call mut methods on it’s contained values and its values need to implement the Copy trait.

Question 13

How can you get access to the value contained in a std::cell::RefCell?

Answer 13

• fn borrow(&self) -> Ref<t></t>
• fn try_borrow(&self) -> Result<ref>, BorrowError&gt;</ref>
• fn borrow_mut(&self) -> RefMut<t></t>
• fn try_borrow_mut(&self) -> Result<refmut>, BorrowMutError&gt;</refmut>

Question 14

What happens when the rules of reference are violated with the help of a RefCell?

Answer 14

The borrow and borrow_mut methods panic.

Question 15

How is the RefMut type used?

Answer 15

RefMut can be used as a mutable reference of the contained type.

Question 16

How can you spawn a new thread?

Answer 16

std::thread::spawn(|| { println!(“hello”); })

the argument is a FnOnce closure