3. Iota

Go has a language feature that, when used with a type definition (and if you squint really hard), kinda looks like an enum (but it's not). It's called iota.

type sendingChannel int

const (
    Email sendingChannel = iota
    SMS
    Phone
)

The iota keyword is a special keyword in Go that creates a sequence of numbers. It starts at 0 and increments by 1 for each constant in the const block. So in the example above, Email is 0, SMS is 1, and Phone is 2.

Go developers sometimes use iota to create a sequence of constants to represent a set of related values, much like you would with an enum in other languages. But remember, it's not an enum. It's just a sequence of numbers.

Assignment

Define an emailStatus type that uses iota syntax to represent the following states:

• EmailBounced: 0

• EmailInvalid: 1

• EmailDelivered: 2

• EmailOpened: 3

package main

type emailStatus int

const (
	EmailBounced = iota
	EmailInvalid
	EmailDelivered
	EmailOpened
)

1

What is a Type?

A type tells Go what kind of data something is.

Examples:

var age int
var name string
var isActive bool

Here:

• int is a type

• string is a type

• bool is a type

Now look at this:

type sendingChannel int

This creates a new custom type.

It is based on int, but it is NOT just an int.

This is important.

It means:

var x sendingChannel

x is its own type. You cannot accidentally assign random integers to it without intention.

This gives your program more safety and clarity.

2

What is a Constant?

A constant is a value that never changes.

Example:

const pi = 3.14159

You cannot reassign it.

Now look at this:

const (
    Email sendingChannel = iota
    SMS
    Phone
)

This creates named constant values.

Instead of using random numbers like:

channel := 2

You use:

channel := Phone

Much clearer.

3

What is iota Actually Doing?

iota is just a counter that resets inside each const block.

This:

const (
    Email sendingChannel = iota
    SMS
    Phone
)

Is the same as writing:

const (
    Email sendingChannel = 0
    SMS   sendingChannel = 1
    Phone sendingChannel = 2
)

That’s it.

It just auto-increments.

Why Use This Instead of Just Numbers?

Because this is bad:

if status == 3 {
    // what is 3?
}

But this is clear:

if status == EmailOpened {
}

Now your code explains itself.

Now Your Assignment

You want:

• EmailBounced: 0

• EmailInvalid: 1

• EmailDelivered: 2

• EmailOpened: 3

So the correct answer is:

type emailStatus int

const (
	EmailBounced emailStatus = iota
	EmailInvalid
	EmailDelivered
	EmailOpened
)