20160101-01.cs

using System;

namespace MyApp
{
    internal enum MyEnum
    {
        Value1,
        Value2,
        Value3,
    }

    public class MyClass
    {
        private MyEnum _myEnum;

        public int Foo(string s)
        {
            if (s == null)
            {
                throw new ArgumentNullException(nameof(s));
            }

            int retVal = 0;

            switch(this._myEnum)
            {
                case MyEnum.Value1:
                case MyEnum.Value2:
                    retVal = 1;
                    break;
                case MyEnum.Value3:
                    retVal = s.Length;
                    break;
            }

            return retVal;
        }
    }
}