C#でDynamicScope

dynamicscope.cs

        [TestMethod]
        public void DynamicScopeTest()
        {
            var x = new User { Name = "hoge" };

            Assert.AreEqual("hoge", x.Name);

            using (DynamicScope.Start(x, y => y.Name, "name"))
            {
                Assert.AreEqual("name", x.Name);
            }

            Assert.AreEqual("hoge", x.Name);
        }

    public static class DynamicScope
    {
        public static IDisposable Start<T, U>(T obj, Expression<Func<T, U>> expression, U value)
        {
            return new DynamicScope<T, U>(obj, expression, value);
        }
    }

    class DynamicScope<TTarget, TValue> : IDisposable
    {
        Action<TTarget, TValue> WriteAction;
        TTarget Target;
        TValue Original;

        public DynamicScope(TTarget obj, Expression<Func<TTarget, TValue>> expression, TValue value)
        {
            var rhs = Expression.Parameter(typeof(TValue), "value");
            var body = expression.Body;
            var assign = Expression.Assign(body, rhs);
            var lhs = expression.Parameters[0];
            var actionExp = Expression.Lambda<Action<TTarget, TValue>>(assign, lhs, rhs);

            WriteAction = actionExp.Compile();
            Original = expression.Compile()(obj);
            Target = obj;

            WriteAction(obj, value);
        }

        public void Dispose()
        {
            WriteAction(Target, Original);
        }
    }