# Union

Union is a data type that combines two or more data types and represents a value of one of those types. Union can combine primitive types, lists, tuples, structures.

Examples:

The type of list items is a union of the types of all items. For example, each element of a List[Int|String] is a string or an integer.

let aList   = [1, 2, "Waves"]               # List[Int|String]
let bList   = [true,false]                  # List[Boolean]
let joined  = aList ++ bList                # List[Boolean|Int|String]

An argument type of the function wavesBalance(Address|Alias): BalanceDetails is a Union of Address and Alias types. You can call a function with an argument of any of these types.
```
wavesBalance(Address(base58'3Mz9N7YPfZPWGd4yYaX6H53Gcgrq6ifYiH7'))
wavesBalance(Alias("merry"))                # The result is the same
```
A return type of the function getInteger(Address|Alias, String): Int|Unit is a Union of Int and Unit types. The function returns an integer value by key from the data storage of a given account, or unit if there is no entry with such a key or the value has a different type.
```
let addr = Address(base58'3N4iKL6ikwxiL7yNvWQmw7rg3wGna8uL6LU')
getInteger(addr,"integerVal")               # Returns 1
getInteger(addr,"noKey")                    # Returns unit
```

# Functions and operators

A value of a Union type cannot be an argument to a function or operator that requires a particular type. For example, the expression

size(getString("key"))

causes a compilation error because the argument type of the function size is String and the return type of the function getString is String|Unit. You can get a value of String type using the getStringValue function.

size(getStringValue("key"))

To get a value of a particular type from a Union, you can use:

Example:

func getAssetName(assetId: ByteVector|Unit) = {
   match assetId {
     case id: ByteVector => assetInfo(id).value().name
     case waves: Unit => "WAVES"
   }
}