What are initializers in Swift?
Swift defines two kinds of initializers for class types to help ensure all stored properties receive an initial value. These are known as designated initializers and convenience initializers. Designated initializers are the primary initializers for a class.
What is the difference between convenience initializer and designated initializer?
A convenience initializer cannot change ANY property before it has called another initializer - whereas a designated initializer has to initialize properties that are introduced by the current class before calling another initializer.
How do I create a convenience initializer in Java?
To define a convenience initializer, we use the convenience keyword before the initializer. For example, In the above example, we have created a designated initializer: init () and a convenience initializer: convenience init (). Inside the convenience initializer, we have called the designated initializer and assigned values to the properties.
Why convenience keyword is needed in Swift?
- Stack Overflow Why convenience keyword is even needed in Swift? Bookmark this question. Show activity on this post. Since Swift supports method and initializer overloading, you can put multiple init alongside each other and use whichever you deem convenient:
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What is convenience in IOS?
A convenience initializer is a secondary initializer that must call a designated initializer of the same class. It is useful when you want to provide default values or other custom setup. A class does not require convenience initializers.
How many types of Initializers are there in Swift?
Designated Initializers and Convenience Initializers Swift defines two kinds of initializers for class types to help ensure all stored properties receive an initial value. Designated initializers are the primary initializers for a class.
What is the purpose of initializers in Swift?
An initializer is a special type of function that is used to create an object of a class or struct. In Swift, we use the init() method to create an initializer. For example, class Wall { ... // create an initializer init() { // perform initialization ... } }
What is Failable initializer in Swift?
A failable initializer creates an optional value of the type it initializes. You write return nil within a failable initializer to indicate a point at which initialization failure can be triggered. ie; if a condition fails, you can return nil . IMPORTANT: In swift, the initializers won't return anything.
What is override init in Swift?
Override initializer In Swift initializers are not inherited for subclasses by default. If you want to provide the same initializer for a subclass that the parent class already has, you have to use the override keyword.
What's the difference between init ?() And init ()?
Notice the initializer is now called init?() to reflect that it returns an optional – the process might return nil if the creation fails. The logic is pretty simple: if there are 11 digits we assume it's correct, otherwise we return nil.
What is Deinit in Swift?
Swift Deinitialization is a process where 'deinitializer' is called to deallocate the memory space before a class instance deallocated. The'deinit' keyword is used to deallocate the memory spaces occupied by the system resources. Deinitialization is available only on class types.
What is the difference between class and struct in Swift?
In Swift, structs are value types whereas classes are reference types. When you copy a struct, you end up with two unique copies of the data. When you copy a class, you end up with two references to one instance of the data. It's a crucial difference, and it affects your choice between classes or structs.
What is self init in Swift?
Note: Swift Optional is not a stored properties. Hence, they need not be initialized. Stored properties are accessed inside the init() method using self property. Note: self is used to refer to the current instance within its own instance methods (Similar to this in java).
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 instance in Swift?
Swift Objects An object is called an instance of a class. For example, suppose Bike is a class then we can create objects like bike1 , bike2 , etc from the class. Here's the syntax to create an object. var objectName = ClassName()
What is required init?
Required initializers will be explained in this article. If we write a required modifier before the definition of init method in a class that indicates that every subclass of that class must implement that initializer. There are various things related to required initializer.
What is class and struct in Swift?
In Swift, structs are value types whereas classes are reference types. When you copy a struct, you end up with two unique copies of the data. When you copy a class, you end up with two references to one instance of the data. It's a crucial difference, and it affects your choice between classes or structs.
What is an initializer list used for?
Initializer List is used in initializing the data members of a class. The list of members to be initialized is indicated with constructor as a comma-separated list followed by a colon. Following is an example that uses the initializer list to initialize x and y of Point class.
How do you call a Deinit in Swift?
A deinitializer is called immediately before a class instance is deallocated. You write deinitializers with the deinit keyword, similar to how initializers are written with the init keyword. Deinitializers are only available on class types....Deinitializationdeinit {// perform the deinitialization.}
What is struct in Swift?
In Swift, a struct is used to store variables of different data types. For example, Suppose we want to store the name and age of a person. We can create two variables: name and age and store value. However, suppose we want to store the same information of multiple people.
What is convenience initializer?
Convenience initializers are also aptly named, and they are initializers used to make initialization a bit easier. Designated initializers tend to set all of the properties up and let the user send in values for each. A convenience initializer often has some of those hard coded, and thus can take less parameters.
What is the difference between convenience initializer and init?
The main difference in their syntax, is that convenience initializers have the convenience keyword before the init. Otherwise they are exactly the same. Once inside our convenience initializer that only takes the sender as a parameter, we just give that parameter to the designated initializer as both the sender and the recipient, since this Message is being used more like a note.
What is a no parameter initializer?
You can see the no-parameter convenience initializer calls the single parameter convenience initializer with a blank content Swift String. That convenience initializer then calls the 2 parameter convenience initializer with the provided content String, and sets the sender parameter to the String “Myself”. Finally that convenience initializer calls the designated initializer for this class with the provided content String, and sets the sender and recipient parameters to the provided “sender” parameter. That fulfills rules 2 and 3. Then there is of course the designated initializer we mentioned earlier that calls its superclass’s designated initializer, fulfilling rule 1.
What are the two types of initializers in Swift?
The Swift language has two different types of initializers they are called designated initializers and convenience initializers. These existed in Objective-C, but a few rules have changed in Swift, and a very helpful keyword was introduced. We will discuss how designated and convenience initializers are used, and how they can work together ...
Why does superclass call subclass implementation?
For instance, if a superclass calls a method that the subclass overrode, the superclass will actually call the subclass’s implementation (since it was overridden). If we didn’t fully initialize our subclass’s properties, and that overridden function relied on them, we would have a bit of a problem.
How many initializers does a class need?
They are the main initializers to be used for a class. A class must have one designated initializer, but it is not limited to one. It can have multiple if necessary, but most classes only have one. Let’s take a look at a designated initializer:
How many rules does Swift have?
Swift has three rules as to how designated and convenience initializers relate to each other. Instead of trying to paraphrase them, I’m just going to quote Apple’s iBook directly:
When are convenience initializers useful?
Note: Convenience Initializers are useful when it comes to assigning default values to stored properties.
What is the init method in Swift?
In Swift, we use the init () method to create an initializer. For example,
How to write a failable initializer?
We write a failable initializer by placing a question mark (?) after the init keyword and return nil if something goes wrong . For example,
What is the initializer in structs?
Here, values inside the parentheses () are automatically assigned to corresponding properties of the struct. This is called a memberwise initializer.
What are the two initializers?
We have also defined two initializers: init () and init (age: Int).
Can Swift initializers be overloaded?
Swift Initializers can be overloaded in a similar way as function overloading.
Does Swift require initializers?
In Swift, we are not required to create an initializer while working with structs. Swift automatically generates a memberwise for us. For example,
How does Swift initialize a class?
In the first phase, each stored property is assigned an initial value by the class that introduced it. Once the initial state for every stored property has been determined, the second phase begins, and each class is given the opportunity to customize its stored properties further before the new instance is considered ready for use.
What is a designated initializer?
Designated initializers are the primary initializers for a class. A designated initializer fully initializes all properties introduced by that class and calls an appropriate superclass initializer to continue the initialization process up the superclass chain.
What happens if a designated initializer doesn't assign a value to an inherited property?
A designated initializer must delegate up to a superclass initializer before assigning a value to an inherited property. If it doesn’t, the new value the design ated initializer assigns will be overwritten by the superclass as part of its own initialization.
How many designated initializers are there in a class?
Classes tend to have very few designated initializers, and it’s quite common for a class to have only one. Designated initializers are “funnel” points through which initialization takes place, and through which the initialization process continues up the superclass chain.
How does initializer delegation work?
The rules for how initializer delegation works, and for what forms of delegation are allowed, are different for value types and class types. Value types (structures and enumerations) don’t support inheritance, and so their initializer delegation process is relatively simple, because they can only delegate to another initializer that they provide themselves. Classes, however, can inherit from other classes, as described in Inheritance. This means that classes have additional responsibilities for ensuring that all stored properties they inherit are assigned a suitable value during initialization. These responsibilities are described in Class Inheritance and Initialization below.
Why does initialization fail?
This failure might be triggered by invalid initialization parameter values, the absence of a required external resource, or some other condition that prevents initialization from succeeding.
What happens if a property takes the same initial value?
If a property always takes the same initial value, provide a default value rather than setting a value within an initializer. The end result is the same, but the default value ties the property’s initialization more closely to its declaration.
Designated Initializers
Convenience Initializers
- Convenience initializers are also aptly named, and they are initializers used to make initialization a bit easier. Designated initializers tend to set all of the properties up and let the user send in values for each. A convenience initializer often has some of those hard coded, and thus can take less parameters. The developer usually write’s a con...
Rules For Designated and Convenience Initializers
- Swift has three rules as to how designated and convenience initializers relate to each other. Instead of trying to paraphrase them, I’m just going to quote Apple’s iBook directly: So you can see our convenience initializer fulfilled rules 2 and 3. Our designated initializer was the top class in the hierarchy (the Message class), so there was no superclass initializer to call (for rule 1). If you rec…
Conclusion
- Designated initializers perform the actual initialization for a class’s properties. Convenience initializers let you program defaults into simpler initializers with less input parameters, and they hand off the actual initialization back to the designated initializers. You don’t have to have any convenience initializers if you wish, but they are quite useful in certain situations. I am particularl…