gistfile1.txt

using System;
using System.Collections.Concurrent;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;
using System.Text;
using System.Web;

public static class QueryStringGenerator
{
    private static readonly ConcurrentDictionary<Type, Delegate> Cache = new();

    public static string ToQuery<T>(this T obj)
    {
        if (obj == null) return "";
        var generator = (Func<T, string>)Cache.GetOrAdd(typeof(T), _ => CreateGenerator<T>());
        return generator(obj);
    }

    private static Func<T, string> CreateGenerator<T>()
    {
        var type = typeof(T);
        var method = new DynamicMethod($"ToQuery_{type.Name}", typeof(string), new[] { type }, typeof(QueryStringGenerator).Module);
        var il = method.GetILGenerator();

        var sb = il.DeclareLocal(typeof(StringBuilder));

        // StringBuilder sb = new StringBuilder();
        il.Emit(OpCodes.Newobj, typeof(StringBuilder).GetConstructor(Type.EmptyTypes)!);
        il.Emit(OpCodes.Stloc, sb);

        var appendMethod = typeof(StringBuilder).GetMethod("Append", new[] { typeof(string) })!;
        var toStringMethod = typeof(object).GetMethod("ToString")!;
        var urlEncodeMethod = typeof(HttpUtility).GetMethod("UrlEncode", new[] { typeof(string) })!;

        var props = type.GetProperties(BindingFlags.Instance | BindingFlags.Public)
                        .Where(p => p.CanRead)
                        .ToArray();

        for (int i = 0; i < props.Length; i++)
        {
            var prop = props[i];

            // sb.Append("?key=") or "&key="
            il.Emit(OpCodes.Ldloc, sb);
            il.Emit(OpCodes.Ldstr, (i == 0 ? "?" : "&") + prop.Name.ToLower() + "=");
            il.Emit(OpCodes.Callvirt, appendMethod);
            il.Emit(OpCodes.Pop); // discard return value

            // value = obj.Prop
            il.Emit(OpCodes.Ldloc, sb);     // sb
            il.Emit(OpCodes.Ldarg_0);       // obj
            il.Emit(OpCodes.Callvirt, prop.GetMethod!); // get value

            if (prop.PropertyType.IsValueType)
                il.Emit(OpCodes.Box, prop.PropertyType);

            // value.ToString()
            il.Emit(OpCodes.Callvirt, toStringMethod);

            // UrlEncode(value)
            il.Emit(OpCodes.Call, urlEncodeMethod);

            // sb.Append(encodedValue)
            il.Emit(OpCodes.Callvirt, appendMethod);
            il.Emit(OpCodes.Pop); // discard return value
        }

        // return sb.ToString()
        il.Emit(OpCodes.Ldloc, sb);
        il.Emit(OpCodes.Callvirt, typeof(StringBuilder).GetMethod("ToString", Type.EmptyTypes)!);
        il.Emit(OpCodes.Ret);

        return (Func<T, string>)method.CreateDelegate(typeof(Func<T, string>));
    }
}