gistfile1.cs

using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace Grades
{
    using CharacterGrade = Grade<char, int>;
    using NumericGrade = Grade<int, int>;

    [TestClass]
    public class GradesTests
    {
        [TestMethod]
        public void GradeTest()
        {
            var grade1 = new CharacterGrade('A', GradeSystems.Letters);
            var grade2 = new NumericGrade(100, GradeSystems.Percentage);

            Assert.AreEqual(grade2.Value, grade1.To<int, PercentageGradeSystem>().Value);
        }
    }

    public class GradeSystems
    {
        public static LetterGradeSystem Letters { get { return new LetterGradeSystem(); } }
        public static PercentageGradeSystem Percentage { get { return new PercentageGradeSystem(); } }
    }

    public abstract class GradeSystem<TValue, TCommon>
    {
        public abstract Grade<TCommon, TCommon> ToCommon(TValue value);
        public abstract Grade<TValue, TCommon> FromCommon(Grade<TCommon, TCommon> common);
    }

    public class LetterGradeSystem : GradeSystem<char, int>
    {
        public override Grade<int, int> ToCommon(char value)
        {
            var index = char.ToUpper(value) - 64;
            return new Grade<int, int>(100 - ((1 - index) * 20), GradeSystems.Percentage);
        }

        public override Grade<char, int> FromCommon(Grade<int, int> common)
        {
            var character = (char)(common.Value + 64);
            return new Grade<char, int>(character, GradeSystems.Letters);
        }
    }

    public class PercentageGradeSystem : GradeSystem<int, int>
    {
        public override Grade<int, int> ToCommon(int value)
        {
            return new Grade<int, int>(value, new PercentageGradeSystem());
        }

        public override Grade<int, int> FromCommon(Grade<int, int> common)
        {
            return new Grade<int, int>(common.Value, new PercentageGradeSystem());
        }
    }

    public class Grade<TValue, TCommon>
    {
        private readonly TValue _value;
        private readonly GradeSystem<TValue, TCommon> _gradeSystem;

        public Grade(TValue value, GradeSystem<TValue, TCommon> system)
        {
            _value = value;
            _gradeSystem = system;
        }

        public TValue Value { get { return _value; } }

        public Grade<TTarget, TCommon> To<TTarget, TTargetSystem>() where TTargetSystem : GradeSystem<TTarget, TCommon>,  new()
        {
            var targetSystem = new TTargetSystem();
            return targetSystem.FromCommon(_gradeSystem.ToCommon(_value));
        }
    }
}