MCQs on Error Handling | Rust

Rust is known for its powerful error handling features, primarily through the Result and Option types, pattern matching, and the ? operator. These concepts ensure safer, more predictable error management. This set of 30 MCQs covers these critical aspects of error handling in Rust, including handling panics.

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Topics:

Result and Option Types

1. Which of the following best describes the Option type in Rust? a) A way to represent success or failure
   b) A container for either Some value or None
   c) A type used for handling exceptions
   d) A type that allows optional parameters
2. What are the two variants of the Result type in Rust? a) Success, Failure
   b) Ok, Err
   c) Some, None
   d) Passed, Failed
3. In Rust, the Option type is primarily used for: a) Returning error messages
   b) Representing possible absence of a value
   c) Handling panics
   d) Wrapping functions with side effects
4. Which variant of Result is used when an operation succeeds in Rust? a) Some
   b) Ok
   c) None
   d) Err
5. What does the None variant of the Option type indicate in Rust? a) A value is available
   b) An error has occurred
   c) No value is present
   d) A panic occurred
6. How do you retrieve a value from an Option safely in Rust? a) Use unwrap()
   b) Use match
   c) Use get()
   d) Use expect()
7. What is the purpose of the Err variant in the Result type in Rust? a) Represents a successful operation
   b) Represents the absence of a value
   c) Represents an error or failure
   d) Represents an empty value
8. When should you use Result instead of Option in Rust? a) When dealing with optional values
   b) When expecting a return value or success/failure
   c) When handling panics
   d) When working with iterators
9. What does Option::map() do in Rust? a) Maps a value inside Some to another value
   b) Maps both Some and None to a default value
   c) Combines Some and None values into a tuple
   d) Allows direct access to the value inside Some
10. Which trait is implemented for both Result and Option types in Rust to allow unwrapping? a) Resultable
    b) Optionable
    c) Unwrap
    d) IntoOption

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Pattern Matching with Result and Option

11. Which Rust construct allows you to handle the variants of Result and Option types? a) if statements
    b) match expressions
    c) for loops
    d) try blocks
12. How can you match on an Option in Rust to handle both Some and None cases? a) Use if let
    b) Use while let
    c) Use match
    d) Use unwrap
13. Which of the following is correct syntax to handle an Err variant in a match expression in Rust? a) match result { Ok(val) => val, Err(e) => e }
    b) match result { Err(e) => e, Ok(val) => val }
    c) match result { Some(val) => val, None => error }
    d) match result { Ok(val) => val, None => error }
14. How do you handle an Option using match to extract the value of Some in Rust? a) match opt { None => return, Some(val) => val }
    b) match opt { Some(val) => val, None => panic!("None found") }
    c) match opt { Some(val) => val, Err(e) => handle_error(e) }
    d) match opt { Some(val) => return val, None => default }
15. What does the match expression do when used with a Result type that is Ok? a) It returns the Err variant
    b) It executes code for the Ok variant
    c) It causes a panic
    d) It wraps the value in Some
16. In Rust, how does pattern matching with Option simplify error handling? a) By allowing you to ignore errors
    b) By combining error handling and value extraction in a single expression
    c) By causing runtime errors
    d) By handling invalid values automatically
17. What happens if you match on an Option but don’t cover both Some and None? a) A compile-time error occurs
    b) The program panics
    c) The None case is assumed
    d) It causes an infinite loop
18. Which of these Rust constructs allows safe handling of an Option that might be None? a) unwrap()
    b) unwrap_or()
    c) match
    d) expect()
19. What is the result of this match expression: match None { Some(x) => x, None => 0 } in Rust? a) It compiles and returns 0
    b) It causes a panic
    c) It returns None
    d) It throws a runtime error
20. What is a common pattern when matching on Result for error handling? a) Always return Ok
    b) Unwrap the result
    c) Handle both Ok and Err variants
    d) Throw an exception

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Propagating Errors with the ? Operator

21. What is the main purpose of the ? operator in Rust? a) To match on results
    b) To propagate errors upwards
    c) To unwrap Option types
    d) To handle panics
22. Which of the following best describes the behavior of the ? operator in Rust? a) It retries the operation on error
    b) It automatically handles all types of errors
    c) It propagates Err from a Result up the call stack
    d) It wraps the result in an Option
23. Which of these is a correct use of the ? operator with Result in Rust? a) let x = some_function()?;
    b) let x = some_function()?; let y = other_function()?;
    c) some_function()? = x;
    d) x = some_function()?
24. What happens when the ? operator encounters an Err value? a) It retries the operation
    b) It wraps the value in Option::None
    c) It returns early from the function with the Err value
    d) It panics with an error message
25. When should you use the ? operator in Rust? a) Only with Option types
    b) When dealing with functions that return Result
    c) For handling panics
    d) To catch all types of runtime errors
26. Which of the following functions will work with the ? operator in Rust? a) Functions that return Option
    b) Functions that return Result
    c) Functions that return Any
    d) Functions that return String
27. What type must a function return for the ? operator to be used within it in Rust? a) Result<T, E>
    b) Option<T>
    c) String
    d) Vec<T>
28. What will happen if you try to use the ? operator in a function that doesn’t return a Result or Option? a) It will cause a compile-time error
    b) The program will panic
    c) The code will silently continue
    d) It will return a None
29. Can you use the ? operator with a panic! call in Rust? a) Yes, it propagates the panic
    b) No, panic! cannot be used with ?
    c) Yes, it turns the panic into an Err
    d) No, ? will suppress the panic
30. How does the ? operator improve error handling in Rust code? a) By converting all errors to panics
    b) By forcing developers to handle every error
    c) By making error propagation more concise and readable
    d) By suppressing all errors

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Answer Key:

Qno	Answer
1	b) A container for either Some value or None
2	b) Ok, Err
3	b) Representing possible absence of a value
4	b) Ok
5	c) No value is present
6	b) Use match
7	c) Represents an error or failure
8	b) When expecting a return value or success/failure
9	a) Maps a value inside Some to another value
10	d) IntoOption
11	b) match expressions
12	c) Use match
13	b) match result { Err(e) => e, Ok(val) => val }
14	b) match opt { Some(val) => val, None => panic!("None found") }
15	b) It executes code for the Ok variant
16	b) By combining error handling and value extraction in a single expression
17	a) A compile-time error occurs
18	c) match
19	a) It compiles and returns 0
20	c) Handle both Ok and Err variants
21	b) To propagate errors upwards
22	c) It propagates Err from a Result up the call stack
23	a) let x = some_function()?;
24	c) It returns early from the function with the Err value
25	b) When dealing with functions that return Result
26	b) Functions that return Result
27	a) Result<T, E>
28	a) It will cause a compile-time error
29	b) No, panic! cannot be used with ?
30	c) By making error propagation more concise and readable