Swift Initialization

When an instance of a class, structure, or enumeration is created it must be provided with some initial values before it is ready to be used. Instance initialization is the process which involves setting up initial value for instance property and to perform any required task to make instance ready to use.

In swift, we have special method called initializers that can take care of whole initialization process. Initializers are invoked automatically when an instance of a particular is created. The Initializers ensure that new instances of a type created is correctly initialized before they are used for the first time.

In swift, an intializer can be created by implementing init() method with zero more parameters, initializers does not mean to return any value.

Swift Initializer Syntax

Syntax:-

Following is the simplest form of an initializer, an instance method with no parameters is created with the init keyword.

Example:-

Here, we have defined a class with two(radius and area) properties and defined a initializer init() method. For radius we have assigned initial value during its declaration and we have calculated area value in initializer init() method, and there is instance method getArea return area value when invoked.

When you run above swift program you will see the following output –

Output:-

Swift Initialization with Parameters

In swift, an intializer init() method is allowed to accept zero more parameters. An intializer init() method with zero more parameters can be defined as following –

Syntax:-

Example:-

Output:-

Swift Initialization with Multiple Initializers

In swift, we are allowed define multiple initializer init() methods, initializer is executed based on argument list.

Example:-

Output:-

Swift Initializer with Parameter Names and Argument Labels

In swift, we are allowed define multiple initializer init() methods. In an initializer parameter names are used to refer parameters internally while argument labels are used when initializer is called. As all the initializers are defined with the same name init, then only way to identify which initializer to be executed is argument list. An initializer is invoked based on the number of arguments, name of arguments or type of arguments.

Initializer Parameters Without Argument Labels

If you want to ignore argument labels in initializer parameters, then you can use underscore (_) instead of an external argument label before particular parameter name.

Swift Optional Property Types

In swift, if we have properties with optional type, those properties are automatically initialized with nil or no value during initialization.

Default Initializers

In swift, class or structure is provided with a default initializer which allows it to set default values for all of its properties. The default initializer creates an instance for class or structure itself that sets default values of its properties.

Example:-

Output:-

Swift Initializer Delegation for Value Types

Initializer delegation is a process in which an intializer is allowed to call another initializers to perform part of an instance’s initialization. Initializer delegation helps to avoid duplicate code across multiple initializers. Initializer delegation works in differently for value types and class types.

Initializer Inheritance and Overriding

In swift a subclasses is not allowed to inherit their superclass initializers by default. If a subclass initializer matches a superclass designated initializer, this way you are providing an override for superclass designated initializer. Therefore, you are required to add override modifier before the subclass’s initializer definition, this is applicable even if you are overriding an automatically provided default initializer.Conversely, if a subclass initializer matches a superclass convenience initializer, you are not required to write override modifier when providing a matching
implementation of a superclass convenience initializer.

Swift Failable Initializer

In swift a class, structure or enumeration initializer may fail for any of the following reason –

• Invalid initialization parameter values
• Absence of required external sources
• Conditions that prevents initializer to succeed

In swift a Failable Initializer allow us to catch and notify initializer method exceptions. The failable initializer can be defined by placing question mark after the init keyword (init?). The failable initializer creates an optional value for the type it is initialized, here a return statement with nil value is used to indicate initialization failure.

Example:-

Output:-

The init! Failable Initializer

The failable initializer created with question mark after init keyword (init?) creates an optional instance of the respective type. In swift there is an alternate way you can create failable initializer by placing an exclamation mark after the init keyword (init!), this way an implicitly unwrapped optional instance is created.

Example:-

Here, we have defined a super class “EmpInfo” and sub class “SalaryInfo” with failable initializers to catch exceptions in super and sub classes. As we discussed if one initializer fail, the entire program stops execution immediately.

When we run the above swift program, we see the following output –

Output:-

Required Initializers

In swift, initializer with required modifier is termed as “Required Initializer“, it tells compiler that we must implement the initializer method in all sub classes.

Example:-

Output:-