Swift Closures Explained

Given a scenario where a closure captures a variable from its surrounding context, but that variable is never mutated by the closure itself nor after the closure's creation, which of the following behaviors does Swift employ as an optimization?

In Swift, closures are always passed by value, ensuring that any modifications made within the closure do not affect the original variables in the enclosing scope.

Describe a scenario in Swift where using an escaping closure that refers to self would necessitate the use of a capture list, and articulate the potential consequences of omitting such a capture list within the context of object lifetime management.

In the context of Swift closures, an ____________ is a closure that is automatically created to wrap an expression being passed as an argument to a function, enabling the omission of braces around the function's parameter and delaying evaluation until the closure is explicitly called.

Match the following Swift closure features with their correct descriptions:

Consider a scenario in Swift where you're using the sorted(by:) method to sort an array of complex objects. The comparison logic necessitates a multi-step calculation involving several properties of each object, resulting in a verbose closure. Which syntactic optimization would most significantly enhance the readability and maintainability of this sorting operation?

In Swift, when a closure captures a variable from its surrounding scope, it always captures a strong reference to it, regardless of whether the closure is escaping or non-escaping.

Explain the nuanced differences in memory management implications when using [weak self] versus [unowned self] in a Swift closure capture list, particularly concerning optionality and potential runtime crashes. Provide a specific scenario illustrating when one is more appropriate than the other.

When defining a function in Swift that accepts multiple closures as arguments, and you intend to utilize trailing closure syntax, you must omit the argument label for the ______ trailing closure, while explicitly labeling all subsequent trailing closures to maintain clarity and disambiguation.

Match each of the following closure syntax features in Swift with its primary benefit:

In the context of Swift, consider a scenario where you have a non-escaping closure being passed as an argument to a function. This closure captures self, which refers to an instance of a class. What is the primary implication of this capture with respect to memory management?

In Swift, autoclosures are typically implemented directly within user code; they are not commonly used in standard library functions due to their inherent complexity and potential for misuse.

Given a scenario where you need to modify a variable captured by a closure within the closure’s body in Swift, elaborate on the specific steps required to ensure that the modification is possible, taking into consideration the immutability of parameters in closures and functions.

In Swift, the keyword ______ is used to indicate that the definition of a closure's parameters and return type has finished, and that the body of the closure is about to begin.

Match the Swift closure type with the descriptions.

Consider a nested function innerFunction defined within outerFunction in Swift. outerFunction has a parameter param. innerFunction captures param. Now, outerFunction returns innerFunction. What happens to the lifetime and accessibility of param?

Shorthand argument names ($0, $1, etc.) can be used in closures regardless of the number of arguments the closure takes.

In Swift, explain the role of the in keyword within a closure expression and detail what precedes and follows it in a typical closure definition.

Swift's automatic reference counting (ARC) system may capture & store a _____ of a value if that value isn’t mutated by a closure, and if the value isn’t mutated after the closure is created.

Match syntax to its function.

Given a sorted(by:) function call on an array of custom objects, where the sorting closure involves a complex calculation that uses several properties of the custom objects, and the goal is to optimize for both performance and code clarity, which of the following strategies is most effective?

If a closure is assigned to multiple constants or variables, each constant or variable contains a completely independent copy of the closure's code and captured state.

Describe a situation in Swift where the use of an autoclosure is particularly advantageous, and clearly explain why it is better suited in that situation than a standard closure.

In Swift, a closure is said to ______ a function when the closure is passed as an argument to the function, but is called after the function returns.

Match a potential issue with the appropriate solution.

In Swift, given a function process(closure: () -> Int) that takes a non-escaping closure, which of the following statements is always true?

Trailing closure syntax can only be used when the closure provided is the very last argument in the function call.

Explain how Swift's compiler uses type inference to simplify closure expressions, and provide a specific example demonstrating how omitting explicit type annotations enhances brevity without sacrificing type safety.

In Swift, when working with closures and memory management, a __________ __________ __________ occurs when two objects (often a class instance and a closure) hold strong references to each other, preventing either from being deallocated by Automatic Reference Counting (ARC).

Match the concept with the correct implementation.

In the context of Swift closures and given the following code snippet:

var x = 0
func outer() -> () -> Void {
  var y = 0
  func inner() {
    x += 1
    y += 1
    print("x: \(x), y: \(y)")
  }
  return inner
}

let a = outer()
let b = outer()
a()
b()
a()

What is the output?

When using trailing closure syntax, you can use multiple trailing closures at once without any labels.

Describe the significance of the order in which closures are called within a function that accepts multiple closures for handling distinct operation outcomes (e.g., success and failure), and how this order impacts the predictability and correctness of program execution.

In Swift, the ______________ method on the Array type takes a closure expression as its single argument, which is called once for each item in the array to create a new one with mapped values.

Please match the escaping closure behaviour to the relevant type.

Consider a situation with a Swift function that takes an escaping closure as an argument and stores it in an array. Later, the function is called multiple times. What best describes the behavior?

If a type can be inferred by using a closure as a function or method argument, one must omit the types.

Compare and contrast the use of closures with that of traditional functions in Swift. What are the main advantages and disadvantages of using closures versus functions?

The ______________ keyword in Swift is used to enable a method inside a struct to modify its properties.

Match the shorthand syntax to the non-shorthand