Getting a ref return value using PropertyInfo

[JamesNK]

    public class RefAndRefReadonlyTestClass
    {
        private int _refField;
        private readonly int _refReadonlyField;

        public RefAndRefReadonlyTestClass(int refReadonlyField)
        {
            _refReadonlyField = refReadonlyField;
        }

        public ref int RefField => ref _refField;

        public ref readonly int RefReadonlyField => ref _refReadonlyField;

        public void SetRefField(int value)
        {
            _refField = value;
        }
    }

    [Test]
    public void GetRefReturnProperty()
    {
        PropertyInfo property = TestReflectionUtils.GetProperty(typeof(RefAndRefReadonlyTestClass), nameof(RefAndRefReadonlyTestClass.RefField));

        RefAndRefReadonlyTestClass c1 = new RefAndRefReadonlyTestClass(123);
        c1.SetRefField(456);

        object v = property.GetValue(c1, null);
    }

The code above throws this exception from PropertyInfo.GetValue: System.NotSupportedException: 'ByRef return value not supported in reflection invocation.'

Can you use a PropertyInfo to get the value of a ref return property?

[EDIT] Add C# syntax highlight by @karelz

[benaadams]

Perhaps related?

Bring back TypedReference https://github.com/dotnet/corefx/issues/14088 (Resolved and part of .NET Standard 2.0)
"Proposal for high-performance codegen-less Reflection factory APIs" https://github.com/dotnet/corefx/issues/24390

Though I assume is a current issue for serializing to and from ref returns?

[benaadams]

Currently it looks like is definately going to ThrowNoInvokeException

Ref returns themselves are an issue with boxing; however...

I think it makes sense that PropertyInfo.GetValue and PropertyInfo.SetValue would operate on the referenced value rather than the reference itself; behaving like FieldInfo.GetValue and FieldInfo.SetValue

And/Or... like FieldInfo should be methods?

public partial class PropertyInfo
{
    public virtual object GetValueDirect(TypedReference obj)
    public virtual void SetValueDirect(TypedReference obj, object value)
}

/cc @VSadov @jkotas

[jkotas]

cc @atsushikan @KrzysztofCwalina @ahsonkhan Span<T> end-to-end gap.

[JamesNK]

There is a difference between getting a ref return by value and by ref, right? (I haven't used ref returns in anger yet so I'm not completely familiar with it)

e.g.

    RefAndRefReadonlyTestClass c1 = new RefAndRefReadonlyTestClass(123);
    c1.SetRefField(456);

    int byValue = c1.RefField;
    ref int byRef = ref c1.RefField;

I would expect PropertyInfo.GetValue to do the first instead of throwing. I would expect there be some way to do the second with PropertyInfo as well. Not every platform has IL generation.

[ghost]

This is a subset of https://github.com/dotnet/corefx/issues/15960 (15960 covers all existing Invoke methods, not just PropertyInfo.GetValue. So I'm closing this as a dupe of that.

[caterpillar-toughb]

Sorry to trouble you folks, but is this working in some form in .NET now?
Looking at this dotnet/coreclr#17639 it would seem to suggest that it's possible.