Union types

The structural union type, written (m1, m2, ...mN), consists of two or more non-union member types containing all possible values of the member types.

(decimal, String)

Restrictions

• Unions never contain the * type.
• Unions contain two or more members.

Default value

The default value of an union type is determined as follows:

1. If it contains void, then undefined.
2. If it contains null, then null.
3. No default value.

Nullability

The following shorthands are available for nullability:

• T? or ?T is equivalent to (null, T).
• T! removes null and/or void from T.