Unions

A union allows you to allow multiple distinct types to be assigned.

For example, either Bytes32 or nil:

type Owner = Bytes32 | nil;

You can assign either of these types to Owner:

let owner: Owner = nil;

But you must narrow the type further through Type Guards before assigning it to its individual types:

let maybe_owner: Owner = nil;

// This fails because the type is too broad
let owner: Bytes32 = maybe_owner;

// This will check at runtime, allowing the type to be narrowed
assert maybe_owner is Bytes32;

// And now this works because we know it's not nil
let owner: Bytes32 = maybe_owner;