A variant is a type that can take on one of a fixed set of values. We define it as a set of values, for example:

type MyVariant = {

The variant type above has two variants: #Black and #White. When we use this type, we have to choose one of the variants. Lets declare a variable of this type and assign the #Black variant value to it.

let myVariant : MyVariant = #Black;

Variants can also have an associated type attached to them. Here's an example of variants associated with the Nat type.

type Person = {
    #Male : Nat;
    #Female : Nat;

let me : Person = #Male 34;

let her : Person = #Female(29);

Note the two equivalent ways of using a variant value. The #Male 34 defines the Nat value separated by the variant with a space. The #Female(29) uses () without a space. Both are the same.

Variants can have different types associated to them or no type at all. For example we could have an OsConfig variant type that in certain cases specifies an OS version.

type OsConfig = {
    #Windows : Nat;
    #Linux : Text;

let linux = #Linux "Ubuntu";

In the case of the #Linux variant, the associated type is a Text value to indicate the Linux Distribution. In case of #Windows we use a Nat to indicate the Windows Version. And in case of #Mac we don't specify any version at all.

Note that the last variable declaration is not type annotated. That's fine, because Motoko will infer the type that we declared earlier.