CommandHandler.cs

using System.Globalization;
using System.Runtime.CompilerServices;

Handler<string, int, string, DateTime, bool>  SomeCommand = 
(arg1, arg2, arg3, arg4, arg5, remainder) =>
{
    Console.WriteLine(arg1);
    Console.WriteLine(arg2);
    Console.WriteLine(arg3);
    Console.WriteLine(arg4);
    Console.WriteLine(arg5);

    Console.WriteLine(string.Join(',', remainder));
};

var rawInput = "/SomeCommand hello 1 world 2024-01-01 true remaining args here";

Dictionary<string, Action<ReadOnlySpan<string?>>> handlers = [];

RegisterHandler(SomeCommand);

var data = rawInput.Split(' ');
var commandNameRaw = data[0];
var arguments = data[1..];

if (!commandNameRaw.StartsWith('/'))
{
    return;
}

var commandName = commandNameRaw[1..].ToLower();

if (!handlers.TryGetValue(commandName, out var handler))
{
    return;
}

handler(arguments);


void RegisterHandler<T1, T2, T3, T4, T5>(
    Handler<T1, T2, T3, T4, T5> handler, 
    [CallerArgumentExpression(nameof(handler))]
    string? handlerName = null
)
    where T1 : IParsable<T1>
    where T2 : IParsable<T2>
    where T3 : IParsable<T3>
    where T4 : IParsable<T4>
    where T5 : IParsable<T5>
{
    var handlerNameInternal = handlerName?.ToLower() ??
        throw new ArgumentNullException(nameof(handlerName));
    
    handlers[handlerNameInternal] = (input) => 
    {
        handler(
            T1.Parse(input[0] ?? "", CultureInfo.InvariantCulture),
            T2.Parse(input[1] ?? "", CultureInfo.InvariantCulture),
            T3.Parse(input[2] ?? "", CultureInfo.InvariantCulture),
            T4.Parse(input[3] ?? "", CultureInfo.InvariantCulture),
            T5.Parse(input[4] ?? "", CultureInfo.InvariantCulture),
            input[5..]
        );
    };
}

delegate void Handler<T1, T2, T3, T4, T5>(
    T1 a, T2 b, T3 c, T4 d, T5 e, ReadOnlySpan<string?> rem
)
where T1 : IParsable<T1>
where T2 : IParsable<T2>
where T3 : IParsable<T3>
where T4 : IParsable<T4>
where T5 : IParsable<T5>;