Guard Swift

What is difference between if let and guard in Swift?

guard let will unwrap an optional for you, but if it finds nil inside it expects you to exit the function, loop, or condition you used it in.

However, the major difference between if let and guard let is that your unwrapped optional remains usable after the guard code..

What is $0 and $1 in Swift?

$0 and $1 are Closure’s first and second shorthand arguments (a.k.a. Shorthand Argument Names or SAN for short). The shorthand argument names are automatically provided by Swift. The first argument can be referenced by $0 , the second argument can be referenced by $1 , the third one by $2 , and so on.

What is a guard condition in UML?

“Guard” is a condition which must be true in order for the trigger to cause the transition. “Effect” is an action which will be invoked directly on the object that owns the state machine as a result of the transition.

What is difference between weak and strong in Swift?

A strong reference means that you want to “own” the object you are referencing with this property/variable. In contrast, with a weak reference you signify that you don’t want to have control over the object’s lifetime. A weak reference is like observing the tree from afar. …

Why we use lazy in Swift?

Lazy properties are also useful when the initial value for a property requires complex or computationally expensive setup that shouldn’t be performed unless or until it’s needed. The example below uses a lazy stored property to avoid unnecessary initialization of a complex class.

Why optionals are useful in Swift?

Optionals are in the core of Swift and exist since the first version of 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.

What is optional binding Swift?

Other than forced unwrapping, optional binding is a simpler and recommended way to unwrap an optional. You use optional binding to check if the optional contains a value or not. If it does contain a value, unwrap it and put it into a temporary constant or variable.

What is if let 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.

What is a lazy VAR in Swift?

Swift has a mechanism built right into the language that enables just-in-time calculation of expensive work, and it is called a lazy variable. These variables are created using a function you specify only when that variable is first requested.

What should be the type of the value of Guard expression?

What should be the type of the value of guard expression? Explanation: The type of result of guard expression should be BOOLEAN which may take only two values either TRUE or FALSE. The statements under guarded block are executed only when the result of guard expression is TRUE.

What are tuples in Swift?

Tuples in Swift occupy the space between dictionaries and structures: they hold very specific types of data (like a struct) but can be created on the fly (like dictionaries). They are commonly used to return multiple values from a function call.

What is @escaping in Swift?

A closure is said to escape a function when the closure is passed as an argument to the function, but is called after the function returns. When you declare a function that takes a closure as one of its parameters, you can write @escaping before the parameter’s type to indicate that the closure is allowed to escape.

What is Guard Swift?

Here’s what the official Swift documentation says about guard : A guard statement is used to transfer program control out of a scope if one or more conditions aren’t met. What it means is that you use guard to exit a function (“transfer control out of scope”) when a condition isn’t met.

How do you use Guard?

The main use of guard statement is to transfer program control out of a scope on certain conditions. These statements are similar with if statements which executes statements based on certain condition (boolean value) but unlike if, the guard statements only run when certain conditions are not met.

What is weak in Swift?

A weak reference is just a pointer to an object that doesn’t protect the object from being deallocated by ARC. In Swift, all weak references are non-constant Optionals (think var vs. … let ) because the reference can and will be mutated to nil when there is no longer anything holding a strong reference to it.

What is reduce in Swift?

Use reduce to combine all items in a collection to create a single new value. The reduce method takes two values, an initial value and a combine closure. For example, to add the values of an array to an initial value of 10.0: let items = [2.0,4.0,5.0,7.0] let total = items.

What is optional type in Swift?

Overview. An optional in Swift is basically a constant or variable that can hold a value OR no value. The value can or cannot be nil. It is denoted by appending a “?” after the type declaration.

What is question mark in Swift?

Question marks after a type refer to Optionals , a way in Swift which lets you indicate the possibility that a value might be absent for any type at all, without the need for special constants.