// @nuget: Z.Expressions.Eval

​

using System;

using Z.Expressions;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        EvalManager.DefaultContext.RegisterType(typeof(MyMath));

        EvalManager.DefaultContext.RegisterAlias("Math", "MyMath");

​

        var decList = new List<decimal>() { 1m };

        var values = new Dictionary<string, object>() { {"X", decList} };

        //EvalManager.DefaultContext.UnregisterStaticMember(typeof(Math));

        //EvalManager.DefaultContext.UnregisterAlias("Math");

        //EvalManager.DefaultContext.UnregisterType(typeof(Math));

​

        Console.WriteLine(Eval.Execute<decimal>("Math.Average(X)", values)); // works

        decList.Clear();

        Console.WriteLine(Eval.Execute<decimal>("Math.Average(X)", values)); // doesn't work when element count = 0, it seems like it's calling System.Math this time?

    }

    public static class MyMath

    {

        public static decimal Average(IEnumerable<decimal> values)

        {

            // in visual studio, a breakpoint here would only be hit if the collection contains > 0 elements.

            // is the default Math class being executed when there are no elements? 

            return values.Any() ? values.Average() : 0m;

        }

    }

}