Variant CSharp

C# implementation of C++ std::variant. An instance of Variant at any given time either holds a value of one of its alternative types, or null. It provides compile-time type safety and highly optimized operations.

✅ JSON serialization with System.Text.Json supported

Usage

Initialization

null (NONE)

Variant<double, string> explicitConstructorWithNullValue = new Variant<double, string>();

double (T1)

Variant<double, string> explicitConstructor = new Variant<double, string>(1d);
Variant<double, string> implicitContructor = 1d;

string (T2)

Variant<double, string> explicitConstructor = new Variant<double, string>("Hello");
Variant<double, string> implicitContructor = "Hello";

Get

T1

Variant<double, string> variant = 1d;
double value = variant.GetT1();
double value = (double)variant;

T2

Variant<double, string> variant = "Hello";
string value = variant.GetT2();
string value = (string)variant;

---

Or use TryGet when type isn't known beforehand

Variant<double, string> variant = 1d;
// T1 = double
if (variant.TryGetT1(out double doubleValue)) // True
{

}
// T2 = string
else if (variant.TryGetT2(out string stringValue)  // False
{

}
// NONE = null
else  // False
{

}

Type Check

Type

Variant<double, string> variant = new Variant<double, string>();
int type = variant.Type; // NONE = 0

Variant<double, string> variant = 1d;
int type = variant.Type; // T1 = 1

Variant<double, string> variant = "Hello";
int type = variant.Type; // T2 = 2

Is<T>

Variant<double, string> variant = 1d;
bool isDouble = variant.Is<double>(); // True
bool isString = variant.Is<string>(); // False

Dealing with collections

It may be useful using the Type property as index for a collection.

T1

int[] array = new int[10];
Variant<double, string> variant = 1d;
int index = variant.GetIndex(); // 0
array[index] = 2;

T2

int[] array = new int[10];
Variant<double, string> variant = "Hello";
int index = variant.GetIndex(); // 1
array[index] = 2;

NONE (null value)

int[] array = new int[10];
Variant<double, string> variant = new Variant<double, string>(); // null
int index = variant.GetIndex(); // -1
if (index == -1)
{
  // Variant is empty!
}

Comparison (by value)

Variant<double, string> variantA = 10d;
Variant<double, string> variantB = 10d;
Variant<double, string> variantC = 17d;

bool areEqual = variantA.Equals(variantB); // True
bool areEqual = variantA.Equals(variantC); // False

Variant<double, string> variantA = "Hello";
Variant<double, string> variantB = "Hello";
Variant<double, string> variantC = "World";

bool areEqual = variantA.Equals(variantB); // True
bool areEqual = variantA.Equals(variantC); // False