MCQs on Closures | Swift

Closures in Swift are self-contained blocks of functionality that can capture values and are widely used for concise, reusable code. Learn syntax, capturing, and escaping to elevate your Swift programming.

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1. Introduction to Closures

1. What are closures in Swift?
   • A) Functions without a name
   • B) Data structures
   • C) Operators for performing operations
   • D) Built-in frameworks
2. Which of the following is a key feature of closures?
   • A) Capturing values from the surrounding context
   • B) Inheriting properties from classes
   • C) Modifying global variables
   • D) Encapsulating external libraries
3. How are closures represented in Swift?
   • A) func keyword
   • B) Curly braces {}
   • C) Parentheses ()
   • D) closure keyword
4. What type of closures are predefined in Swift?
   • A) Global functions and nested functions
   • B) Anonymous classes
   • C) Closure variables
   • D) External dependencies
5. In which scenarios are closures commonly used?
   • A) Callback mechanisms
   • B) Variable initialization
   • C) Data persistence
   • D) Error handling
6. Which keyword indicates that a closure is escaping?
   • A) @escaping
   • B) @closure
   • C) @capture
   • D) @return

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2. Capturing Values

7. What does a closure capture by default in Swift?
   • A) References to constants and variables from its surrounding scope
   • B) Only global variables
   • C) Memory addresses
   • D) Return values of functions
8. How do closures capture values in Swift?
   • A) By making copies of the values
   • B) By referencing the memory of surrounding variables
   • C) By creating temporary objects
   • D) By using external pointers
9. What happens to captured variables in closures when their scope ends?
   • A) They persist as long as the closure exists
   • B) They are destroyed
   • C) They are reset to default values
   • D) They are moved to global scope
10. How can a closure modify a captured variable?
    • A) By using inout
    • B) By declaring the variable as mutable
    • C) By default, captured variables cannot be modified
    • D) By copying the variable into the closure
11. Can closures capture multiple variables from their surrounding scope?
    • A) Yes, there is no limit
    • B) No, only one variable at a time
    • C) Yes, but only constants
    • D) No, closures cannot capture variables
12. What kind of memory management issue can closures create if not handled properly?
    • A) Strong reference cycles
    • B) Memory fragmentation
    • C) Dangling pointers
    • D) Stack overflow

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3. Closure Syntax and Shorthand Arguments

13. What is the correct syntax for a closure in Swift?
    • A) { (parameters) -> ReturnType in code }
    • B) [parameters -> ReturnType : code]
    • C) (parameters, code) => ReturnType
    • D) { parameters : ReturnType : code }
14. What can be omitted in a closure if Swift can infer the type?
    • A) Parameter types and return type
    • B) Curly braces {}
    • C) The in keyword
    • D) The entire closure body
15. How are shorthand argument names represented in Swift closures?
    • A) $0, $1, $2
    • B) _0, _1, _2
    • C) arg0, arg1, arg2
    • D) @0, @1, @2
16. What does the in keyword in a closure signify?
    • A) The start of the closure’s body
    • B) Variable initialization
    • C) Capturing of values
    • D) Ending the closure
17. Can closures return values in Swift?
    • A) Yes, closures can have return types
    • B) No, closures are only for executing code
    • C) Yes, but only Bool values
    • D) No, closures cannot have outputs
18. What is the shortest form of a closure in Swift?
    • A) { $0 + $1 }
    • B) { (a: Int, b: Int) -> Int in a + b }
    • C) { (Int, Int) -> Int in code }
    • D) { return $0 }

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4. Closures as Function Parameters

19. How are closures passed as parameters in Swift?
    • A) As arguments using their syntax
    • B) By reference only
    • C) By wrapping them in functions
    • D) By using closure: prefix
20. Which syntax declares a function that accepts a closure parameter?
    • A) func example(closure: () -> Void)
    • B) closure example(Void -> Void)
    • C) func example() -> closure {}
    • D) example(func closure)
21. What is a trailing closure in Swift?
    • A) A closure passed outside the function’s parentheses
    • B) A closure that executes last in a program
    • C) A closure attached to a return value
    • D) A closure with no parameters
22. Which keyword is used for multiple closures as function parameters?
    • A) None, closures are added sequentially
    • B) They are separated by commas
    • C) @chaining
    • D) closure+
23. Can a closure parameter have a default value?
    • A) Yes, like other parameters
    • B) No, closures must always be defined
    • C) Yes, but only if it returns Void
    • D) No, closures cannot be optional
24. What is the primary benefit of passing closures as parameters?
    • A) Enables higher-order functions
    • B) Reduces memory usage
    • C) Eliminates the need for variables
    • D) Ensures thread safety

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5. Escaping and Non-Escaping Closures

25. What is an escaping closure?
    • A) A closure that is executed after a function returns
    • B) A closure that cannot capture values
    • C) A closure that modifies global variables
    • D) A closure that is self-referential
26. How are non-escaping closures executed?
    • A) Before the function exits
    • B) After the function returns
    • C) They are ignored
    • D) Only in global context
27. Which keyword is used to define an escaping closure?
    • A) @escaping
    • B) @closure
    • C) @async
    • D) @return
28. Why might an escaping closure cause a retain cycle?
    • A) It creates a strong reference to self
    • B) It does not release variables properly
    • C) It modifies global objects
    • D) It returns void
29. Which of the following is NOT true about escaping closures?
    • A) They can outlive the function’s execution
    • B) They require explicit syntax
    • C) They can only be synchronous
    • D) They can introduce reference cycles
30. What is the main difference between escaping and non-escaping closures?
    • A) Escaping closures are executed later, non-escaping closures are executed immediately
    • B) Non-escaping closures cannot be passed into functions
    • C) Escaping closures always return a value
    • D) Non-escaping closures are not supported in Swift

Here are the answers again in the tabular format:

Qno	Answer
1	A) Functions without a name
2	A) Capturing values from the surrounding context
3	B) Curly braces {}
4	A) Global functions and nested functions
5	A) Callback mechanisms
6	A) @escaping
7	A) References to constants and variables from its surrounding scope
8	B) By referencing the memory of surrounding variables
9	A) They persist as long as the closure exists
10	A) By using inout
11	A) Yes, there is no limit
12	A) Strong reference cycles
13	A) { (parameters) -> ReturnType in code }
14	A) Parameter types and return type
15	A) $0, $1, $2
16	A) The start of the closure’s body
17	A) Yes, closures can have return types
18	A) { $0 + $1 }
19	A) As arguments using their syntax
20	A) func example(closure: () -> Void)
21	A) A closure passed outside the function’s parentheses
22	B) They are separated by commas
23	A) Yes, like other parameters
24	A) Enables higher-order functions
25	A) A closure that is executed after a function returns
26	A) Before the function exits
27	A) @escaping
28	A) It creates a strong reference to self
29	C) They can only be synchronous
30	A) Escaping closures are executed later, non-escaping closures are executed immediately