Classes

Classes

Classes serve as a template to define characteristics and behaviors of an object.

They are reference types, meaning all instances of a class carry the same characteristics and behaviors.

An instance is an object created based on a class.

Syntax

In Swift, classes are defined using the class keyword, followed by a class name, and a pair of curly braces {}.

class MyClass {
// Class body
}

Note: Class names should be capitalized as per convention.

var, init(), and func

Variables can be defined with the following steps:

  1. Use the var keyword.
  2. Provide a variable name.
  3. Assign a value with =.

init() is a special method that gets called when a class instance is created. It can take any number of arguments in the form of property: DataType. The self keyword refers to the instance itself.

Functions within a class are defined with the following steps:

  1. Use the func keyword.
  2. Name the function.
  3. Provide a set of curly braces {} to hold the function’s body.
class Employee {
var name = ""
var salary = 0
var manager = false
init(name: String, salary: Int) {
self.name = name
self.salary = salary
}
func promote() {
self.manager = true
}
}

In the code above, Employee class is given three properties or variables:

  • A name set to an empty string "".
  • A salary set to an integer value of 0.
  • A manager boolean value set to false.

The init() method takes in name and salary arguments that are of data type string and integer, respectively.

When called on an instance, the .promote() method will set its manager property to true.

Creating an Instance

In Swift, the init() method is called when a class instance is created.

An employee by the name of "Sandy Cheeks" works for “Tree Dome Enterprises Limited” and makes a salary of 10,000 acorns a year. Below, the sandyCheeks variable is assigned to the value of Employee(). This creates an instance of the class Employee.

Sandy’s name and salary are set through the initialization method:

var sandyCheeks = Employee(name: "Sandy Cheeks", salary: 10000)

Note: Classes are also named types, which are types that are given a name when defined and can be referred to as such (i.e. instances of Employee have the type Employee).

Access Functions and Variables

To view an instance’s characteristics or properties:

print(sandyCheeks.name)
// Output: Sandy Cheeks
print(sandyCheeks.salary)
// Output: 10000

Sandy is getting a promotion! So the .promote() method will be called on sandyCheeks instance:

print(sandyCheeks.manager)
// Output: false
sandyCheeks.promote()
print(sandyCheeks.manager)
// Output: true
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