You Don’t Know iota

Explains Go’s iota, its uses in constants, enums, and bitwise operations, with tips and best practices.

4 min readJun 30, 2025

Preface

When you delve into official libraries, open-source libraries, or any Go project, you’ll find the magical identifier iota everywhere. It plays an important role, making code more concise and clear, while improving readability and maintainability. Its applications are wide-ranging, from enumerated types to bit operations, and even complex constant expression calculations—it can do it all.

In this article, I will take you on an in-depth exploration of the magical power of iota, including an introduction to iota, its use cases, practical tips, and important considerations.

Introduction to iota

Within a constant declaration, the predeclared identifier iota represents successive untyped integer constants. Its value is the index of the respective ConstSpec in that constant declaration, starting at zero.

The above quote is from the official documentation. In short, by using iota, we can automatically create a series of consecutive integers in constant declarations, starting from zero, without manually specifying the value for each constant.

Use Cases for iota

Automatically Generating Incrementing Constant Values

With iota, it’s easy to generate incrementing constant values. The first constant using iota in a constant declaration is initialized to 0, and subsequent constants automatically increment, making it unnecessary to specify the value of each constant manually when defining a series of incrementing constants. This improves code readability and maintainability. For example:

const (
    Apple  = iota // 0
    Banana        // 1
    Cherry        // 2
)

Defining Enumerated Type Constants

By using iota, you can easily define a series of related enumerated values without having to manually specify the number for each value. This makes the enumeration type definitions more concise and easier to extend or modify. For example:

type WeekDay int

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

Expression Calculation

By using iota within constant declarations, you can create complex expressions and adjust the value of iota as needed in each constant declaration. This allows you to easily generate a set of constants that follow a specific pattern. For example:

const (
    _  = iota
    KB = 1 << (10 * iota) // 1 << (10 * 1) = 1024B = 1KB
    MB = 1 << (10 * iota) // 1 << (10 * 2) = 1048576B = 1MB
    GB = 1 << (10 * iota) // 1 << (10 * 3) = 1073741824B = 1GB
    TB = 1 << (10 * iota) // 1 << (10 * 4) = 1099511627776B = 1TB
)

Bitwise Operations

By combining the left shift operator (<<) with iota, you can conveniently generate a set of constants for bitwise operations. For example:

const (
    FlagNone  = 0         // 0
    FlagRead  = 1 << iota // 1
    FlagWrite             // 2
    FlagExec              // 4
)

Tips and Considerations When Using iota

Skipping Values

We can use the underscore (_) to ignore certain values, for example:

const (
    Apple = iota // 0
    _
    Banana // 2
)

iota Is Independent in Different Constant Blocks

The scope of iota is the entire constant block. The iota in different constant blocks is independent, and the value of the first iota in each block is always 0.

const (
    A = iota // 0
    B        // 1
)

const (
    C = iota // 0
    D        // 1
)

Summary

This article provided a detailed introduction to iota. By fully leveraging the features of iota in your code, you can make your code more concise and clear, while also improving readability and maintainability.