Swift gives us an alternative to if let called guard let , which also unwraps optionals if they contain a value, but works slightly differently: guard let is designed to exit the current function, loop, or condition if the check fails, so any values you unwrap using it will stay around after the check.
What is difference between guard and if let in Swift?
With guard let you are creating a new variable that will exist in the current scope. With if let you’re only creating a new variable inside the code block.
What is if let in Swift?
The “if let” allows us to unwrap optional values safely only when there is a value, and if not, the code block will not run. Simply put, its focus is on the “true” condition when a value exists.
How do I use optionals in Swift?
You can simply represent a Data type as Optional by appending ! or ? to the Type . If an optional contains a value in it, it returns value as Optional
What are optionals in Swift?
An Optional is a type on its own, actually one of Swift 4’s new super-powered enums. It has two possible values, None and Some(T), where T is an associated value of the correct data type available in Swift 4.
Why do we need optionals in Swift?
An optional value allows us to write clean code with at the same time taking care of possible nil values. If you’re new to Swift you might need to get used to the syntax of adding a question mark to properties. Once you get used to them you can actually start benefiting from them with, for example, extensions.
What is GCD in IOS Swift?
Grand Central Dispatch (GCD) is a low-level API for managing concurrent operations. It can help improve your app’s responsiveness by deferring computationally expensive tasks to the background. It’s an easier concurrency model to work with than locks and threads.
What means nil in Swift?
In Swift, nil means the absence of a value. Sending a message to nil results in a fatal error. An optional encapsulates this concept. An optional either has a value or it doesn’t.
What is force unwrapping in Swift?
It’s the action of extracting the value contained inside an Optional . This operation is dangerous because you are telling the compiler: I am sure this Optional value does contain a real value, extract it!
What is unconditional unwrapping in Swift?
Unconditional Unwrapping
When you’re certain that an instance of Optional contains a value, you can unconditionally unwrap the value by using the forced unwrap operator (postfix ! ). For example, the result of the failable Int initializer is unconditionally unwrapped in the example below.
How many ways unwrap optional?
You can unwrap optionals in four ways: With force unwrapping, using if optional != nil and optional! With optional binding, using if let constant = optional {
Why we use closures in Swift?
Closures can capture and store references to any constants and variables from the context in which they’re defined. This is known as closing over those constants and variables. Swift handles all of the memory management of capturing for you.
What are blocks in Swift?
Closures in Swift
Closures are self-contained blocks of functionality that can be passed around and used in your code. Closures in Swift are similar to blocks in C and Objective-C and to lambdas in other programming languages.
Is Swift synchronous or asynchronous?
Although Swift functions are synchronous by default, we can make them asynchronous by adding one keyword: async . Inside asynchronous functions, we can call other asynchronous functions using a second keyword: await . As a result, you’ll often hear Swift developers talk about async/await as a way of coding.
What is multithreading in Swift?
Multithreading can be defined as the process which facilitates the CPU to create and execute concurrent threads. Typically, a CPU performs one operation at a time.
What is data type in Swift?
Swift offers a collection of built-in data types which are string, integer, floating-point numbers, and Booleans. These data types are also found in most programming languages.
What is double in Swift?
The Double data type is the standard Swift way of storing decimal numbers such as 3.1, 3.14159 and 16777216.333921.
What is optional binding and optional chaining in Swift?
Optional binding stores the value that you’re binding in a variable. 2. Optional chaining doesn’t allows an entire block of logic to happen the same way every time. 2. Optional binding allows an entire block of logic to happen the same way every time.
How do I unwrap a string in Swift?
Various ways to unwrap an optional in Swift
- Forced unwrapping — unsafe. let a:String = x!
- Implicitly unwrapped variable declaration — unsafe in many cases. var a = x!
- Optional binding — safe.
- Optional chaining — safe.
- Nil coalescing operator — safe.
- Guard statement — safe.
- Optional pattern — safe.
What does += mean in Swift?
Like C, Swift provides compound assignment operators that combine assignment ( = ) with another operation. One example is the addition assignment operator ( += ): var a = 1. a += 2. // a is now equal to 3.
What is string interpolation in Swift?
String interpolation is a way to construct a new String value from a mix of constants, variables, literals, and expressions by including their values inside a string literal. You can use string interpolation in both single-line and multiline string literals.
Can any be optional Swift?
Swift doesn’t allow comparing Optional
How does Swift handle optional?
To use an optional, you “unwrap” it
An optional String cannot be used in place of an actual String . To use the wrapped value inside an optional, you have to unwrap it. The simplest way to unwrap an optional is to add a ! after the optional name. This is called “force unwrapping”.
How do I unwrap an array in Swift?
I can force unwrap it in a short way: var arrayForCrash = arrayOfOptionals. map { $0! }
What is binding in Swift?
A binding in SwiftUI is a connection between a value and a view that displays and changes it. You can create your own bindings with the @Binding property wrapper, and pass bindings into views that require them.
What is @published Swift?
@Published is one of the property wrappers in SwiftUI that allows us to trigger a view redraw whenever changes occur. You can use the wrapper combined with the ObservableObject protocol, but you can also use it within regular classes.
What is capture list in Swift?
Capture lists: The list of values that you want to remain unchanged at the time the closure is created. Capturing values: If you use external values inside your closure, Swift stores them alongside the closure. This way they persist even when the external part of the code no longer exists.
What is callback function in Swift?
Callbacks are functions that often take the form of a closure (basically an in-line function with no name that’s passed as a parameter to another function), but they could technically be a named function. Perhaps it’s easiest to see in code itself.
What is generic in Swift?
Swift Generics allows us to create a single function and class (or any other types) that can be used with different data types. This helps us to reuse our code.
What is trailing closure in Swift?
A trailing closure is written after the function call’s parentheses, even though it is still an argument to the function. When you use the trailing closure syntax, you don’t write the argument label for the closure as part of the function call.
Can we extend struct Swift?
It is not possible to subclass a struct in Swift, only classes can be subclassed. An extension is not a subclass, it’s just adding additional functionality on to the existing struct , this is comparable to a category in Objective-C.
What is mutating in Swift?
Essentially, a function that’s been marked as mutating can change any property within its enclosing value. The word “value” is really key here, since Swift’s concept of structured mutations only applies to value types, not to reference types like classes and actors.
What is mutex in Swift?
When designing concurrent programs, correctness is always the most important factor, but you should also consider performance factors as well. Code that executes correctly under multiple threads, but slower than the same code running on a single thread, is hardly an improvement.
What is Dispatch main async?
To summarize, DispatchQueue. async allows you to schedule work to be done using a closure without blocking anything that’s ongoing. In most cases where you need to dispatch to a dispatch queue you’ll want to use async .
What is the async code in Swift?
An asynchronous function in Swift can give up the thread that it’s running on, which lets another asynchronous function run on that thread while the first function is blocked. When an asynchronous function resumes, Swift doesn’t make any guarantee about which thread that function will run on.
What is Dispatchqueue in Swift?
Dispatch queues are FIFO queues to which your application can submit tasks in the form of block objects. Dispatch queues execute tasks either serially or concurrently. Work submitted to dispatch queues executes on a pool of threads managed by the system.
What is queue in Swift?
The Swift queue is the same as any other programming language. The queue is a data structure used to store element; in the queue, we can store data from one end and delete it using another end. Queue works and follows FIFO, which means first in, first out.
How many types of threads are there in Swift?
As I understand there are 3 types of DispatchQueue in swift: Main (serial) (Main Thread) Global (Concurrent) (Background Threads working in parallel) Custom (Concurrent or serial)
What is constructor in Swift?
In Swift, an initializer is a special function that we use to create objects of a particular class, struct, or other type. Initializers are sometimes called constructors, because they “construct” objects.
What is self init Swift?
Swift provides a default initializer for any structure or class that provides default values for all of its properties and doesn’t provide at least one initializer itself. The default initializer simply creates a new instance with all of its properties set to their default values.
What is the difference between none and null?
None means Nothing, Nothing is a concept that describes the absence of anything at all. Nothing is sometimes confused with Null, but they are very different concepts because Nothing means absence of anything, while Null means unknown (you do not know if there is a thing or not).
Why is it nil instead of zero?
Another name for 0 that is used in sports is “nil”. This is derived from the Latin word “nihil”, which means “nothing”. Although common in British English, in football results and the like, it is only used infrequently in U.S. English.
What are collection types in Swift?
Swift provides three primary collection types, known as arrays, sets, and dictionaries, for storing collections of values. Arrays are ordered collections of values. Sets are unordered collections of unique values. Dictionaries are unordered collections of key-value associations.
What is primitive in Swift?
In Swift, String is “primitive” in that it’s the standard string type used by all text-related functions in the standard library. But there’s no compiler magic keeping you from making your own string types that can be created with literals or handled with operators.
What is type safe in Swift?
Swift is a type-safe language. A type safe language encourages you to be clear about the types of values your code can work with. If part of your code expects a String, you can’t pass it an Int by mistake.
Is var a datatype in Swift?
In this tutorial, you will learn about data types in Swift programming with the help of examples. Here, Int is a data type that specifies that the num variable can only store integer data.
Swift Data Types.
| Data Types | Example | Description |
|---|---|---|
| Bool | true and false | Any of two values: true or false |
What is a declaration in Swift?
A declaration introduces a new name or construct into your program. For example, you use declarations to introduce functions and methods, to introduce variables and constants, and to define enumeration, structure, class, and protocol types.
What is force unwrapping in Swift?
It’s the action of extracting the value contained inside an Optional . This operation is dangerous because you are telling the compiler: I am sure this Optional value does contain a real value, extract it!
How do I use optionals in Swift?
You can simply represent a Data type as Optional by appending ! or ? to the Type . If an optional contains a value in it, it returns value as Optional
What is the difference between if let and guard let in Swift?
In if let , the defined let variables are available within the scope of that if condition but not in else condition or even below that. In guard let , the defined let variables are not available in the else condition but after that, it’s available throughout till the function ends or anything.
How many ways unwrap optional?
You can unwrap optionals in four ways: With force unwrapping, using if optional != nil and optional! With optional binding, using if let constant = optional {
What is optional binding in Swift?
Optional binding is a mechanism built into Swift to safely unwrap optionals. Since an optional may or may not contain a value, optional binding always has to be conditional. To enable this, conditional statements in Swift support optional binding, which checks if a wrapped value actually exists.