Swift Functions, Closures, and Data Structures: Key Concepts for Students

What is a function in Swift?

A named, reusable block of logic that can take parameters and return a value.

How do you call a Swift function with argument labels?

By using the parameter labels in the function call, such as add(a: 3, b: 4).

What is a closure in Swift?

An unnamed block of code that can be stored, passed, or returned like a value.

How are closures different from functions when called?

They do not use argument labels when called.

What is trailing closure syntax in Swift?

A syntax that allows the last closure parameter to be written outside the parentheses.

What is the full syntax for a Swift closure?

{ (params) -> ReturnType in code }

What is the simplified closure syntax when there are no parameters or return value?

{ code }

What is the type of the Swift function sayHello()?

() -> Void

Write a closure that takes two integers and returns their product.

let multiply = { (a: Int, b: Int) -> Int in return a * b }

What is wrong with this code: print(add(a: 3, b: 4))?

Argument labels cannot be used when calling it.

Why is _ used in a Swift closure parameter list?

It ignores an incoming value that is not needed.

How do you convert a closure parameter into trailing closure syntax?

Move the closure outside the parentheses when it is the final parameter.

What is a function in Swift?

A reusable block of code.

What is a method in Swift?

A function that belongs to a class, struct, or enum.

Can a struct contain methods in Swift?

Yes, it can contain functions inside it.

What are the two main uses of return in Swift?

To exit early or send back a value.

What happens when return is used before a print statement?

The print statement never runs.

What is wrong with this code: guard let name else { print("No name") }?

A control transfer statement such as return is missing.

What does randomElement() do in Swift?

It selects a random item from a collection and returns an optional.

Why is force unwrapping randomElement() risky?

It can crash if the collection is empty.

What does this code print: let result = names.randomElement() ?? "Z"?

A random element from the array.

What is optional unwrapping in Swift?

Retrieving the actual value from an optional.

What is forced unwrapping in Swift?

Using ! to directly access an optional value.

Why is optional binding safer than forced unwrapping?

It safely checks for nil before accessing the value.

What does the nil-coalescing operator ?? do?

It provides a default value if nil appears.

What does this code print: let value = Double(input ?? "10") ?? 0.0 when input is nil?

10.0

How do you safely convert a String? to Double using optional binding?

if let value = input, let d = Double(value) { print(d) }

What is a tuple in Swift?

A fixed group of related values.

Can tuples store different data types?

Yes, they can contain multiple types.

How do you access values in an unnamed tuple?

Using indexes like .0 or .1.

How do you access values in a named tuple?

Using property names like student.name.

What is tuple destructuring?

Splitting grouped values into separate variables.

What is the difference between sorted() and sort()?

One creates a new sorted array, while the other changes the original array.

Does sorted() modify the original array?

No, it leaves the original unchanged.

Does sort() create a new array?

No, it changes the existing array directly.

What does this code print: numbers.sorted { a, b in return a < b }?

The array in ascending order.

What is a UISlider in UIKit?

A UI control that lets the user choose a value by dragging.

What data type does UISlider.value return?

Float

What is a UIStepper in UIKit?

A UI control that increases or decreases a value using buttons.

What data type does UIStepper.value return?

Double

What is a struct in Swift?

A value type that can contain properties and methods.

What happens when you assign one struct variable to another?

A separate copy is created.

What is a class in Swift?

A reference type that supports shared objects.

What happens when you assign one class object to another variable?

Both variables point to the same object.

What is a computed property in Swift?

A property that calculates its value instead of storing it.

What is the default setter parameter name in Swift?

newValue

What is an instance method?

A function used with a specific object.

What is a type method in Swift?

A function that belongs to the type itself.

How do you define a type method in Swift?

Using static func or class func.

What does this code print: p2.name after changing p3.name when both reference the same class object?

The updated name value.

What happens when p.nextYearAge = 30 if the setter sets age = newValue - 1?

The age becomes 29.

When should you use an enum in Swift?

When working with a fixed set of related cases.

What does filter() do in Swift?

Creates a new array with elements that match a condition.

Does filter() modify the original array?

No, it returns a new one.

What does contains(where:) return?

A Boolean value.

Does contains(where:) return the matching element?

No, only true or false.

What does becomeFirstResponder() do?

Makes a UI control active, often showing the keyboard.

What does resignFirstResponder() do?

Makes a UI control inactive, often hiding the keyboard.

What is an extension in Swift?

A way to add new functionality to an existing type.

Can extensions add stored properties?

No, only computed properties can be added.

What is an instance property in an extension?

A property used with a specific value or object.

What is a type property in an extension?

A property that belongs to the type itself and uses static.

How do you access a type property in an extension?

By using the type name directly.

What is a protocol in Swift?

A blueprint that defines required properties and methods.

Can protocols contain stored properties?

No, only requirements can be declared.

What must a type do to adopt a protocol?

Implement all required properties and methods.

Can a class adopt multiple protocols?

Yes, multiple blueprints can be adopted.

Why are protocols useful in Swift?

They help create reusable and flexible code.

What is the role of UITableViewDataSource?

Providing row counts and cell content.

What is the role of UITableViewDelegate?

Handling user interaction and behavior.

What does tableView(_:numberOfRowsInSection:) do?

It tells how many rows should appear.

What does tableView(_:cellForRowAt:) do?

It creates and configures each visible cell.

Why is dequeueReusableCell used in UITableView?

To reuse cells and improve performance.

What does the is keyword do in Swift?

Checks whether a value matches a specific type.

What is upcasting in Swift?

Converting a subclass reference into a superclass reference.

What is downcasting in Swift?

Converting a superclass reference into a subclass reference.

What is the difference between as? and as!?

One safely returns an optional, while the other force casts and may crash.

What is Any in Swift?

A type that can store any value.

What is AnyObject in Swift?

A type that can store only class instances.

Can a struct be stored in AnyObject?

No, only class types are allowed.

What is optional chaining in Swift?

Safely accessing properties or methods through optionals.

What are the three common ways to transfer data in iOS?

Direct passing, delegate pattern, and notifications.

What is property passing in iOS?

Sending data directly through a variable.

Why is weak used for delegates?

To avoid memory leaks and strong reference cycles.

What does NotificationCenter.default.post do?

Broadcasts a message to listeners.

What does NotificationCenter.default.addObserver do?

Listens for broadcasted messages.

What is a dictionary in Swift?

A collection of unordered key-value pairs.

Why does dictionary access return an optional?

The requested key may not exist.

What happens when you set a dictionary key to nil?

The key-value pair is removed.

What does updateValue(_:forKey:) do in a dictionary?

It updates an existing value or adds a new one.