Golang Iota for Enumerations

Go has an interesting way to alias enumeration values using the iota keyword. Iota helps increment integer values inside your block or declaration. Consider the following code:

type Gender int
const(
        UNKNOWN Gender = 0
        FEMALE = 1
        MALE = 2
)

Using the iota keyword you can instead alias your values:

type Gender int
const(
        UNKNOWN Gender = iota
        FEMALE = iota
        MALE = iota
)

The first use of iota within the factor block returns 0. Whenever iota is used again on a new line it is incremented by 1. So FEMALE = 1, MALE = 2. A new const block or declaration will initialize iota back to 0.

You can further shorten this by just invoking iota once:

type Gender int
const(
        UNKNOWN Gender = iota
        FEMALE
        MALE
)

This has the same effect as assigning the individually on each line. You can also skip numbers like so:

type Color int
const(
        WHITE Color = iota 
        RED                  
        ORANGE         
        YELLOW
        _
        _
        GREEN
        BLUE
        PURPLE
)

In the above example WHITE is 0, YELLOW is 3, and GREEN is 6 (because the two _ lines skip 4 and 5).

Why do this? Well in Go you cannot easily interchange integers and custom types in functions; however, you can with integer constants. Go treats integer constants loosely until they’re used in a strict context. You can check out Katrin Owen’s article (https://splice.com/blog/iota-elegant-constants-golang/ ) which goes into details about this technique for writing elegant constants.