Builds a Delegate from MethodInfo?

To be honest, if you don’t know the type at compile time, there isn’t a huge amount of benefit in creating a Delegate. You don’t want to use DynamicInvoke; it will be about as slow as reflection. The main exception to this is when there is a delegate-type lurking in the shadows, for example when subscribing to an event – in which case EventInfo makes this available.

For info, in .NET 3.5 on Expression, there is:

Expression.GetActionType(params Type[] typeArgs);
Expression.GetFuncType(params Type[] typeArgs)

That might help to an extent:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
static class Program {
    static void Main() {
        DoStuff("Test1");
        DoStuff("Test2");
    }
    static void DoStuff(string methodName) {
        MethodInfo method = typeof(Program).GetMethod(methodName);
        List<Type> args = new List<Type>(
            method.GetParameters().Select(p => p.ParameterType));
        Type delegateType;
        if (method.ReturnType == typeof(void)) {
            delegateType = Expression.GetActionType(args.ToArray());
        } else {
            args.Add(method.ReturnType);
            delegateType = Expression.GetFuncType(args.ToArray());
        }
        Delegate d = Delegate.CreateDelegate(delegateType, null, method);
        Console.WriteLine(d);
    }
    public static void Test1(int i, DateTime when) { }
    public static float Test2(string x) { return 0; }
}