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❮ Swift Access Control Swift Literals ❯

Swift Constants

Once set, the value of a constant cannot be changed during program execution.

Constants can be of any data type such as integer constants, floating-point constants, character constants, or string constants. There are also constants of enumeration types:

Constants are similar to variables, but the difference is that the value of a constant cannot be changed once set, whereas the value of a variable can be changed at will.

Constant Declaration

Constants are declared using the keyword let, with the following syntax:

let constantName = <initial value>

Below is an example of using a constant in a simple Swift program:

import Cocoa

let constA = 42
print(constA)

The output of the above program is:

42

Type Annotation

You can add a type annotation when declaring a constant or variable to specify the type of value the constant or variable can store. To add a type annotation, follow the constant or variable name with a colon and a space, then the type name.

var constantName:<data type> = <optional initial value>

Below is a simple example demonstrating the use of type annotation in Swift constants. Note that a constant must be initialized when defined:

import Cocoa

let constA = 42
print(constA)

let constB:Float = 3.14159

print(constB)

The output of the above program is:

42
3.14159

Constant Naming

Constant names can consist of letters, numbers, and underscores.

Constants must start with a letter or an underscore.

Swift is a case-sensitive language, so uppercase and lowercase letters are considered different.

Constant names can also use simple Unicode characters, as shown in the following example:

import Cocoa

let _const = "Hello, Swift!"
print(_const)

let 你好 = "你好世界"
print(你好)

The output of the above program is:

Hello, Swift!
你好世界

Constant Output

Variables and constants can be output using the print function (print replaced println in Swift 2).

Constants can be inserted into a string using parentheses and a backslash, as shown in the following example:

import Cocoa

let name = "tutorialpro.org"
let site = "http://www.tutorialpro.org"

print("\(name)'s website address is: \(site)")

The output of the above program is:

tutorialpro.org's website address is: http://www.tutorialpro.org
❮ Swift Access Control Swift Literals ❯