System.Text.Json does not support constructors with byref parameters.

[mattchidley]

Description

I have a List of objects whose constructors take 'in' parameters of DateTime and TimeSpan.

public class TestClass
    {
        public TestClass(in DateTime dateTime, in TimeSpan timeSpan)
        {
            DateTime = dateTime;
            TimeSpan = timeSpan;
        }

        public DateTime DateTime { get; set; }

        public TimeSpan TimeSpan { get; set; }
    }

When serializing a list of these objects, I am seeing the exception in the title being thrown:

This is specifically being thrown at IEnumerableDefaultConverter.cs line 255:

state.Current.DeclaredJsonPropertyInfo = state.Current.JsonClassInfo.ElementClassInfo!.PropertyInfoForClassInfo;

Unfortunately I have absolutely no clue what the issue is here. I'm hoping you might be able to help.

[Dotnet-GitSync-Bot]

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[GrabYourPitchforks]

Looks like System.Text.Json doesn't understand byrefs as ctor arguments? You can work around this for now by removing the in keyword from your ctor parameters.

[ilanb1996]

Hi @GrabYourPitchforks
Im looking for an issue to take as my fist contribution and stumbled upon this issue.
Do you think its ok if i take it on me?

[GrabYourPitchforks]

@layomia - thoughts?

[layomia]

@GrabYourPitchforks, @ilanb1996 sounds good, thanks! I'll assign the issue to you - please tag me with any questions.

[eiriktsarpalis]

Out of curiosity, what should be our expected approach to fixing this? I presume the error occurs when attempting to instantiate SmallObjectWithParameterizedConstructorConverter<> with DateTime& as a type parameter. Presumably we'd have to fall back to LargeObjectWithParameterizedConstructorConverterWithReflection?

[eiriktsarpalis]

Once we address this issue we should make sure to re-enable the following disabled test:

runtime/src/libraries/System.Text.Json/tests/Common/ConstructorTests/ConstructorTests.ParameterMatching.cs

Lines 1295 to 1301 in 1a0c9ca

	[Fact]
	[ActiveIssue("https://github.com/dotnet/runtime/issues/34779")]
	public async Task BindingBetweenRefProps()
	{
	string json = @"{""NameRef"":""John""}";
	await Serializer.DeserializeWrapper<TypeWith_RefStringProp_ParamCtor>(json);
	}