MCQs on Ownership and Borrowing | Rust

Rust’s ownership and borrowing system is a fundamental feature that ensures memory safety without a garbage collector. It prevents data races and ensures efficient memory usage through strict rules on ownership, borrowing, and references.

Topics Overview:

• Ownership rules: move, borrow, clone
• References and borrowing
• Mutable vs immutable references
• The concept of “ownership” in Rust

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MCQs on Ownership and Borrowing in Rust

1. Ownership Rules: Move, Borrow, Clone

1. In Rust, when an object is moved, it:
   • A) Can be used again by the original owner
   • B) Transfers ownership to another variable, invalidating the original variable
   • C) Copies the data to another variable
   • D) Is not allowed to be accessed again
2. What does the clone method in Rust do?
   • A) It moves the ownership of an object
   • B) It creates a deep copy of the object
   • C) It borrows the object for temporary use
   • D) It references the object without copying
3. Which of the following actions in Rust is considered a “move” operation?
   • A) Assigning an object to a new variable
   • B) Using clone to copy an object
   • C) Borrowing an object immutably
   • D) Passing an object to a function by reference
4. Which of these does not violate ownership rules in Rust?
   • A) Borrowing a value mutably and immutably at the same time
   • B) Moving a value to another variable
   • C) Cloning a value and using it after cloning
   • D) Returning a reference to a local variable
5. When a variable is moved in Rust, the original variable:
   • A) Retains ownership of the data
   • B) Becomes a reference to the data
   • C) Is no longer accessible
   • D) Can be cloned without restrictions

2. References and Borrowing

6. In Rust, borrowing refers to:
   • A) Transferring ownership of a value
   • B) Creating a reference to a value without taking ownership
   • C) Copying a value to another variable
   • D) Creating a mutable clone of a value
7. Which of the following is a valid way to borrow a value in Rust?
   • A) let x = &y;
   • B) let x = y.clone();
   • C) let x = y;
   • D) let x = &mut y;
8. What is the difference between a mutable and immutable reference in Rust?
   • A) A mutable reference allows changes to the value, while an immutable reference does not
   • B) An immutable reference allows changes to the value, while a mutable reference does not
   • C) Both allow changes to the value
   • D) Neither reference allows changes to the value
9. What happens if you try to borrow a value mutably and immutably at the same time in Rust?
   • A) It compiles without errors
   • B) The mutable reference is allowed to coexist with immutable references
   • C) The program will fail to compile
   • D) The mutable reference is discarded
10. Which of the following best describes a reference in Rust?
    • A) A copy of a value stored in a new variable
    • B) A pointer to a value that does not take ownership
    • C) A value that is moved to another variable
    • D) A way to modify a value directly

3. Mutable vs Immutable References

11. In Rust, you can have multiple immutable references to a value at the same time, but:

• A) You can only have one mutable reference at a time
• B) You can have multiple mutable references at the same time
• C) Immutable references cannot coexist with mutable references
• D) Mutable references can coexist with immutable references

12. Which of the following can modify the value of a variable in Rust?

• A) Immutable reference
• B) Borrowing a variable immutably
• C) Mutable reference
• D) Moving the variable

13. What does Rust enforce when you have a mutable reference to a value?

• A) No other references (mutable or immutable) can exist at the same time
• B) The reference is automatically cloned
• C) Other variables can modify the value
• D) The value is moved to another variable

14. Which scenario will cause a compilation error in Rust?

• A) Borrowing a value immutably multiple times
• B) Borrowing a value mutably and immutably at the same time
• C) Using a mutable reference when no other references exist
• D) Returning a mutable reference from a function

15. Can you have mutable and immutable references to the same value in Rust at the same time?

• A) Yes, because Rust allows mixed references
• B) No, Rust ensures this would cause a compile-time error
• C) Yes, but only if the references are in different threads
• D) No, Rust allows this if you use clone

4. The Concept of “Ownership” in Rust

16. In Rust, the concept of ownership ensures that:

• A) Every value has exactly one owner
• B) A value can be shared between multiple owners
• C) Memory is automatically freed without explicit control
• D) Ownership can be transferred without any restrictions

17. What happens when ownership of a value is moved in Rust?

• A) The value is cloned to the new owner
• B) The original owner can no longer access the value
• C) The ownership is transferred but both owners can access it
• D) The value is automatically borrowed

18. Which of the following is true regarding ownership in Rust?

• A) Ownership can be shared across threads
• B) A variable can own multiple values simultaneously
• C) Ownership of a value can be transferred without affecting its data
• D) When a value goes out of scope, its memory is automatically freed

19. Which action violates Rust’s ownership rules?

• A) Cloning a value before using it
• B) Returning ownership of a value from a function
• C) Moving a value to another variable and using the original variable
• D) Borrowing a value immutably

20. What is the result of calling move on a value in Rust?

• A) The value is cloned and the original is still usable
• B) The value is moved, and the original reference becomes invalid
• C) The ownership is shared between two variables
• D) The value is automatically freed from memory

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Answer Key:

Qno	Answer (Option with Text)
1	B) Transfers ownership to another variable, invalidating the original variable
2	B) It creates a deep copy of the object
3	A) Assigning an object to a new variable
4	C) Cloning a value and using it after cloning
5	C) Is no longer accessible
6	B) Creating a reference to a value without taking ownership
7	A) let x = &y;
8	A) A mutable reference allows changes to the value, while an immutable reference does not
9	C) The program will fail to compile
10	B) A pointer to a value that does not take ownership
11	A) You can only have one mutable reference at a time
12	C) Mutable reference
13	A) No other references (mutable or immutable) can exist at the same time
14	B) Borrowing a value mutably and immutably at the same time
15	B) No, Rust ensures this would cause a compile-time error
16	A) Every value has exactly one owner
17	B) The original owner can no longer access the value
18	D) When a value goes out of scope, its memory is automatically freed
19	C) Moving a value to another variable and using the original variable
20	B) The value is moved, and the original reference becomes invalid