C# Reflection get Field or Property by Name

Question

Is there a way to supply a name to a function that then returns the value of either the field or property on a given object with that name? I tried to work around it with the null-coalesce operator, but apparently that doesn't like different types (which is also a bit weird to me because null is null). I could separate it it out into if nulls, but there has to be a better way to do this. Here is my function, and the two lines with Comparison objects don't compile, but I will leave them in there to show what I am trying to do.

private void SortByMemberName<T>(List<T> list, string memberName, bool ascending)
{
   Type type = typeof (T);
   MemberInfo info = type.GetField(memberName) ?? type.GetProperty(memberName);

   if (info == null)
   {
        throw new Exception("Member name supplied is neither a field nor property of type " + type.FullName);
   }

   Comparison<T> asc = (t1, t2) => ((IComparable) info.GetValue(t1)).CompareTo(info.GetValue(t2));
   Comparison<T> desc = (t1, t2) => ((IComparable) info.GetValue(t2)).CompareTo(info.GetValue(t1));

    list.Sort(ascending ? asc : desc);
}

I have heard of something called dynamic LINQ that could be used, but for the sake of learning, I am doing it my way.

Answer 1

Change this line:

MemberInfo info = type.GetField(memberName) ?? type.GetProperty(memberName);

to this:

MemberInfo info = type.GetField(memberName) as MemberInfo ??
    type.GetProperty(memberName) as MemberInfo;

because there's no implicit cast to the base class when using the ternary operator like that. The ternary requires that the types of all outputs be the same.

Answer 2

As of C# 9.0, this will finally be possible:

Target typed ?? and ?:

Sometimes conditional ?? and ?: expressions don’t have an obvious shared type between the branches. Such cases fail today, but C# 9.0 will allow them if there’s a target type that both branches convert to:

Person person = student ?? customer; // Shared base type
int? result = b ? 0 : null; // nullable value type

That means the code block in the question will also compile without errors; it will 'see' that FieldInfo and PropertyInfo have a shared base type, MemberInfo.

MemberInfo info = type.GetField(memberName) ?? type.GetProperty(memberName);