Section 1
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Bridging Headers
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Last updated
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Date created
Mar 14, 2020
Cards (73)
Section 1
(50 cards)
Bridging Headers
Classes
What is the difference between the two property observers?
willSet changes a property to newValue that is what a value will be, and didSet changes a property toan oldValue. This allows you to track changing values
Closures
What are generics and what problem do they solve?
Generics are used to make algorithms safely work with types. In Swift, generics can be used both in functions and data types, e.g. in classes, structures or enumerations. Generics solve the problem of code duplication. A common case is when you have a method that takes a type of parameter and you have to duplicate it just to accommodate a parameter of another type.
What is the difference between a local and global variable?
Global variables are defined outside of any function, method, or closure, and local variables are those defined within functions, methods, or closures.
Generics (types, functions, and constraints)
What is a static method?
A method usable by a class, not a specific instance (object) of that class.
If you copy a struct and then alter the property of the copy, does the original change? Why or why not?
The original doesnt change, because structs are value types. The copy us a copy of the values, not the reference.
What is a type parameter?
Type parameters specify and name a placeholder type, and are written immediately after the function's name between angle brackets. Example:
There are a few cases when you can't avoid using implicitly unwrapped optionals. When? Why?
The most common reasons to use implicitly unwrapped optionals are: When a property that is not nil by nature cannot be initialized at instantiation time. A typical example is an Interface Builder outlet, which always initializes after its owner has been initialized. In this specific case -- assuming it's properly configured in Interface Builder -- the outlet is guaranteed to be non-nil before it's used. To solve the strong reference cycle problem, which is when two instances refer to each other and require a non-nil reference to the other instance. In such a case, one side of the reference can be marked unowned, while the other uses an implicitly unwrapped optional.
What is generic programming?
A way to write functions and data types without being specific about the types they use. As an example, an Array can take any type of object.
Under the hood, what type of data structure is an optional?
An optional is an enum! enum Optional<T> { case None case Some(T) }
What is an optional and what problem do optionals solve?
An optional is used to let a variable of any type represent the lack of value. In Objective-C, the absence of value is available in reference types only, and it uses the nil special value. Value types, such as int or float, do not have such ability. Swift extends the lack of value concept to both reference and value types with optionals. An optional variable can hold either a value or nil any time.
Extensions
How do you force unwrap an optional?
With an ! This forces an optional to unwrap... even if it has no value!
How do you optionally unwrap an optional?
if let This essentially says, "if this optional returns a value, put that value into a new variable"
Sets vs. Arrays (when and why?)
What is a tuple?
A tuple is an on-the-fly data structure that resembles a struct or a mini-dictionary, designed to be discarded and only hold data as a small data structure. The best part about it is that it can return multiple pieces of data in one return from a method.
What is an optional?
A variable that might return a nil value.
Is this correct? var optional1: String? = nil var optional2: String? = .None optional1 == optional2
What is the word for the instance of a class?
An object
Methods
Enums
What are the two types of property observers?
didSet and willSet
What is an important difference about Swift classes and structures regarding polymorphism?
Classes can inherit from other classes, but structs cannot.
What is a computed property?
A property that is determined by code
What is wrong with this code? public struct ThermometerStruct { private(set) var temperature: Double = 0.0 public mutating func registerTemperature(temperature: Double) { self.temperature = temperature } } let thermometerStruct = ThermometerStruct() thermometerStruct.registerTemperature(56.0)
thermometerStruct is declared via let, but the .registerTemperature(temperature) method mutates the field. In structures, methods that change the internal state must be marked as mutating but invoking them from immutable variables is not allowed.
What are static methods and properties in swift?
"properties and methods that belong to a type, rather than to instances of a type." Excerpt From: Hudson, Paul. "Hacking with Swift." iBooks. This material may be protected by copyright.
Optionals (regular, implicit, and unwrapping)
Swift Playgrounds
Error Handling
What type are structs?
Value type
Value types vs. reference types
Value types are objects that point at values, while reference types just point to an address
Swift API Design Guidelines
Structs
A struct is a complex data type that contains properties. When you create a struct, xcode creates an init method and allows you to construct instances. Properties are accessed via dot notation.
What is the nil coalescing operator?
An operator (??) that helps unwrap optionals or set them to a default. So if you have var brian = Person; var name = brian.name ?? "First Name Unknown"
When should you use a structure, and when should you use a class?
There's an ongoing debate about whether using classes over structures is a good or bad practice. Functional programming tends to favor value types, whereas object-oriented programming prefers classes. In Swift, classes and structures differ by a number of features. You can sum up the differences as follows: Classes support inheritance, structures don't Classes are reference types, structures are value types There's no universal rule that determines what's best to use. The general recommendation is to use the most minimal tool required to accomplish your goal, but a good rule of thumb is to use structures unless you need inheritance or reference semantics.
Swift.org
What is a closure's capture list?
A capture list is the list of variables captured by a variable on declaration. So let closure = { [thing] in print("I love \(thing)") } The capture list is [thing]. Because this closure is being declared with thing, it captures it when this declaration happens.
Do Swift classes get automatic memberwise initializers?
Nope, you gotta write your own init method.
Protocols
Why can force unwrapping be bad?
Because you can unwrap an optional that will return nil.
If you copy a class object and then alter the property of the copy, does the original change? Why or why not?
Yep it changes! Because the copy is a reference to the values, as classes are reference types.
What is different about Swift and ObjC Strings?
Objective-C Strings are encoded in UTF-16, 16bit strings where accents and characters are saved as separate characters.
What type are classes?
Reference types
Initializers(single and multiple)
What is the difference between as? and as! In typecasting?
as? Is optional typecasting, meaning you think a cast can occur, while as! forces a cast
Variables vs. Constants
You set variables as "var" and the value can change. You set constants as "let" and the value will never change.
What does this mean? var optional2: String? = .None
This is the correct way to intialize an optional as nil. Optionals are just enums behind the scenes.
Section 2
(23 cards)