Swift Variables and Constants

In Swift, variables and constants are fundamental building blocks for storing and manipulating data. They play a crucial role in managing information throughout your program.

Variables

Variables are containers that hold values which can be changed during program execution. They are declared using the var keyword.

var age = 25
age = 26 // Value can be changed

Constants

Constants, on the other hand, hold values that cannot be modified once they are assigned. They are declared using the let keyword.

let pi = 3.14159
// pi = 3.14 // This would result in an error

Type Inference and Explicit Type Declaration

Swift uses Type Inference to automatically determine the data type of a variable or constant based on its initial value. However, you can also explicitly declare the type:

var name: String = "John"
let height: Double = 1.75

When to Use Variables vs Constants

• Use variables when the value needs to change over time
• Use constants for values that should remain fixed
• Prefer constants by default for better code safety and performance

Naming Conventions

Swift uses camelCase for naming variables and constants. Names should be descriptive and meaningful:

let maximumLoginAttempts = 3
var currentLoginAttempt = 0

Multiple Declaration

You can declare multiple variables or constants of the same type in a single line:

var x = 0.0, y = 0.0, z = 0.0

Type Safety

Swift is a type-safe language. This means you can't assign a value of one type to a variable or constant of another type. For more information, see Swift Type Safety.

Optionals

In Swift, you can use Optionals to represent the absence of a value. This is particularly useful when working with variables that might not have a value:

var possibleNumber: Int? = nil
possibleNumber = 42

Best Practices

• Use meaningful and descriptive names for variables and constants
• Prefer constants over variables when the value won't change
• Use type inference when possible, but explicitly declare types when needed for clarity
• Consider using optionals when a variable might not have a value

Understanding variables and constants is crucial for effective Swift programming. They form the foundation for more advanced concepts like Swift Data Types and Swift Operators.