Constants in Golang

What are Constants?

In Go, a constant is a value that cannot be changed once it's defined. Unlike variables, constants are determined at compile time, which means they are immutable and have several unique properties that set them apart from regular variables.

Basic Constant Declaration

Here's the simplest way to declare a constant in Go:

const pi = 3.14159
const greeting = "Hello, World!"

Types of Constants

Go supports several types of constants:

1. Typed Constants

When you specify a type explicitly, you create a typed constant:

const age int = 30
const temperature float64 = 98.6

2. Untyped Constants

Go also supports untyped constants, which are more flexible:

const x = 42         // untyped integer constant
const message = "Go" // untyped string constant

Untyped constants can be used more freely and are converted to the appropriate type when used.

Constant Declarations

Go provides multiple ways to declare constants:

Single Constant Declaration

const maxConnections = 100

Multiple Constant Declarations

const (
    statusOK = 200
    statusNotFound = 404
    statusServerError = 500
)

Constant Expressions

Constants can be created using expressions that are evaluated at compile-time:

const (
    secondsPerMinute = 60
    minutesPerHour = 60
    secondsPerHour = secondsPerMinute * minutesPerHour
)

Iota: The Constant Generator

iota is a special identifier in Go used for creating incrementing constants:

const (
    Sunday = iota    // 0
    Monday           // 1
    Tuesday          // 2
    Wednesday        // 3
    Thursday         // 4
    Friday           // 5
    Saturday         // 6
)

Common Pitfalls to Avoid

• Don't use constants for values that might change at runtime.

• Be cautious when using iota in complex scenarios.

• Remember that constants are compile-time constructs.