aldaviva / uniontypes

⚭︎ Union types implemented in C# using implicit casts

UnionTypes

Introduction

A union type is a type whose value can be any one of a specific set of types. For example, you may define a union type whose value must be either an int or a string.

Once defined, you can use instances of this union in a type safe way. For example, if you want a list that can contain only string and int values, but no other types, you can create a List<T> whose generic type is your new union type, instead of making a List<object> that could allow values of other types to be added. This way, you don't have to check whether or not each value is either a string or int when you read them, because it's statically guaranteed at compile time.

Usage

Dependencies

This package is available on NuGet Gallery.

It can run in .NET Standard 2.0 runtimes and later, as well as .NET Framework 4.5.2 and later.

dotnet add package UnionTypes

Writing

using UnionTypes;

Union<string, int> myUnion = "hi";

IList<Union<string, int>> path = ["xConfiguration", "Network", 1, "DNS", "Server", 3, "Address"];
string message = string.Join(' ', path); // "xConfiguration Network 1 DNS Server 3 Address"

Type alias

You can make the type more readable by aliasing a meaningful name to it. This is a C# 12 feature.

using XPathSegment = Union<string, int>;

IList<XPathSegment> path = ["xConfiguration", "Network", 1, "DNS", "Server", 3, "Address"];

Reading

For each of the union's constituent types, you can test if the value of an instance of the union type is of that constituent type with the HasValue1 and other properties, or ValueIndex. You can get the strongly-typed value with the related Value1 and other properties.

if (path[0].HasValue1) {
    string message = $"First item is the string {path[0].Value1}"; // "First item is xConfiguration"
}

if (path[0] is { HasValue1: true, Value1: var firstItem }) {
    string message = $"First item is {firstItem?.Trim()}"; // "First item is xConfiguration"
}

if (path[0].ValueIndex == Union2Index.Value1) {
    string message = $"First item is the string {path[0].Value1}"; // "First item is xConfiguration"
}

string message = path[0] switch {
    { ValueIndex: Union2Index.Value1, Value1: var first } => $"First item is string {first?.Trim()}",
    { ValueIndex: Union2Index.Value2, Value2: var first } => $"First item is int {Math.Abs(first)}",
};

If you don't need the value to be strongly typed, you can get it as an object using the Value property.

Console.WriteLine($"{path[0].ValueType} {path[0].Value}); // System.String xConfiguration

Union size

This library allows unions of 2 or more types, up to a maximum limit of 16 types.