ProxySample/ProxyableConsole/IProxyable.cs

IProxyable.cs

using System;

namespace ProxyableConsole
{
    public interface IProxyable : IProxyable<object>
    {
        new void Execute();
    }

    class BodyProxyable : BodyProxyable<object>, IProxyable
    {
        public BodyProxyable(Action execute) : base(() =>
            {
                execute?.Invoke();
                return null;
            })
        {
        }

        void IProxyable.Execute() => Execute();
    }

    class AspectProxyable : AspectProxyable<object>, IProxyable
    {
        public AspectProxyable(IProxyable source, Action<Action> execute) : base(source, f =>
            {
                execute?.Invoke(() => f());
                return null;
            })
        {
        }

        void IProxyable.Execute() => Execute();
    }

    public static class Proxyable
    {
        public static IProxyable<TResult> Body<TResult>(Func<TResult> execute) => new BodyProxyable<TResult>(execute);
        public static IProxyable Body(Action execute) => new BodyProxyable(execute);

        public static IProxyable<TResult> Aspect<TResult>(this IProxyable<TResult> source, Func<Func<TResult>, TResult> execute) => new AspectProxyable<TResult>(source, execute);
        public static IProxyable Aspect(this IProxyable source, Action<Action> execute) => new AspectProxyable(source, execute);
    }
}

Program.cs

using System;

namespace ProxyableConsole
{
    class Program
    {
        static void Main(string[] args)
        {
            Proxyable.Body(() => Console.WriteLine("Body"))
                .Aspect(a =>
                {
                    Console.WriteLine("Before");
                    a();
                    Console.WriteLine("After");
                })
                .Execute();
        }
    }
}