public static void Swap<T>(Expression<Func<T>> left, Expression<Func<T>> right)
{
    var lexpr = (MemberExpression) left.Body;
    var rexpr = (MemberExpression) right.Body;
    var lvalue = left.Compile()();
    Set(lexpr.Member, lexpr.Expression != null ? Expression.Lambda(lexpr.Expression).Compile().DynamicInvoke() : null, right.Compile()());
    Set(rexpr.Member, rexpr.Expression != null ? Expression.Lambda(rexpr.Expression).Compile().DynamicInvoke() : null, lvalue);
}

private static void Set(MemberInfo member, Object self, Object value)
{
    if (member is FieldInfo)
    {
        ((FieldInfo) member).SetValue(self, value);
    }
    else // PropertyInfo
    {
        ((PropertyInfo) member).SetValue(self, value, null);
    }
}

public static int X { get; set; }
public static int Y { get; set; }

static void Main(string[] args)
{
    X = 123;
    Y = 456;
    Swap(() => X, () => Y);
    Console.WriteLine("X = {0}, Y = {1}", X, Y);
}