Amber Documentation

Union Types

Union types provide a flexible way to define function parameters and return types that can accept values of multiple distinct types.

Function Parameters

One of the most common use cases for union types is defining flexible function parameters. This allows functions to accept different types without resorting to dynamic typing:

fun print_value(val: Int | Text | Bool) {
    echo(val)
}

print_value(42)       // Valid
print_value("Amber")  // Valid
print_value(true)     // Valid

You can also use union types with multiple parameters:

fun describe(a: Int | Text, b: Bool | Num) {
    echo("First: {a}, Second: {b}")
}

describe(10, true)           // Valid
describe("hello", 3.14)     // Valid
describe("test", false)      // Valid

You can also use match expressions for more complex type narrowing:

fun analyze(data: Int | Text | Bool) {
    if {
        data is Int: echo("Got an integer")
        data is Text: echo("Got text: {data}")
        data is Bool: echo("Got a boolean")
    }
}

Return Types

Union types are also useful for function return types, allowing functions to return different types based on their execution:

fun parse_input(input: Text): Int | Text {
    if input == "" {
        return "Empty input"
    }
    return 0
}

let result = parse_input("42")

Arrays

Union types work seamlessly with arrays, allowing you to pass different types of arrays:

fun array_type(items: [Int] | [Text]): Text {
    if items is [Int] {
        return "Int array: {items}"
    } else {
        return "Text array: {items}"
    }
}

echo(array_type([1, 2, 3]))
// Returns: Int array: 1 2 3

For more information on related topics, see Type System, Data Types, and Functions.

Type Condition

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Type System