❔ Enum with data

I'm working on a lexer, and I'm encountering this problem where I need to associate different data with different token types. My first attempt was this:

internal enum TokenKind
{
    A,
    B,
    C
}

internal struct Token
{
    private TokenKind kind;

    // Optional properties depending on which token kind
    internal long? AData { get; }
    internal string? BData { get; }
    internal bool? CData { get; }
}

internal enum TokenKind
{
    A,
    B,
    C
}

internal struct Token
{
    private TokenKind kind;

    // Optional properties depending on which token kind
    internal long? AData { get; }
    internal string? BData { get; }
    internal bool? CData { get; }
}

then you can use it like so:

switch (token.kind)
{
    case TokenKind.A:
        // Do something with AData
        Console.WriteLine(token.AData!);
        break;
    case TokenKind.B:
        // Do something with BData
        Console.WriteLine(token.BData!);
        break;
    case TokenKind.C:
        // Do something with CData
        Console.WriteLine(token.CData!);
        break;
}

switch (token.kind)
{
    case TokenKind.A:
        // Do something with AData
        Console.WriteLine(token.AData!);
        break;
    case TokenKind.B:
        // Do something with BData
        Console.WriteLine(token.BData!);
        break;
    case TokenKind.C:
        // Do something with CData
        Console.WriteLine(token.CData!);
        break;
}

I kind of dislike this implementation though. For one it seems kind of messy with the null-forgiving stuff, but it also makes the token type very bulky since it requires a separate field for every data variant. Since there will be a ton of tokens, it's important to minimize their size.

It's also error-prone in the sense that someone can try to read data without first checking the token kind.

What I'm trying to do is conceptually this:

enum TokenKind {
  A(i64),
  B(String),
  C(bool),
}

enum TokenKind {
  A(i64),
  B(String),
  C(bool),
}

It doesn't have to look like this, but this is the kind of behavior I'm looking for (Rust enums, or algebraic sum types for those who know).

What would be the clean way to make this in C#? Bear in mind There is actually a lot of token kinds, and not all token kinds have data associated with them (in fact the majority do not).

❔ Enum with data

I'm working on a lexer, and I'm encountering this problem where I need to associate different data with different token types. My first attempt was this:

internal enum TokenKind
{
    A,
    B,
    C
}

internal struct Token
{
    private TokenKind kind;

    // Optional properties depending on which token kind
    internal long? AData { get; }
    internal string? BData { get; }
    internal bool? CData { get; }
}

internal enum TokenKind
{
    A,
    B,
    C
}

internal struct Token
{
    private TokenKind kind;

    // Optional properties depending on which token kind
    internal long? AData { get; }
    internal string? BData { get; }
    internal bool? CData { get; }
}

then you can use it like so:

switch (token.kind)
{
    case TokenKind.A:
        // Do something with AData
        Console.WriteLine(token.AData!);
        break;
    case TokenKind.B:
        // Do something with BData
        Console.WriteLine(token.BData!);
        break;
    case TokenKind.C:
        // Do something with CData
        Console.WriteLine(token.CData!);
        break;
}

switch (token.kind)
{
    case TokenKind.A:
        // Do something with AData
        Console.WriteLine(token.AData!);
        break;
    case TokenKind.B:
        // Do something with BData
        Console.WriteLine(token.BData!);
        break;
    case TokenKind.C:
        // Do something with CData
        Console.WriteLine(token.CData!);
        break;
}

enum TokenKind {
  A(i64),
  B(String),
  C(bool),
}

enum TokenKind {
  A(i64),
  B(String),
  C(bool),
}

❔ Enum with data

❔ Enum with data

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