Introspection Deserialization

Syntec

Hey, I am having an issue with Introspection and deserialization. Lets say I have some class with primitive properties and properties which are classes.

The deserialization function works on primitives no issues using FieldInfo.SetValue, the deserialization function is recursive so the the below code is the most important snippet for my issue. I broke classOut into a separate variable for testing purposes. The Function is Deserialize(dataIn As String) As Object

Initial Calling of Deserialize from a button.press event

Var loadTest As New TestClass
loadTest = TestClass(SEC.Load("some file path to serialized data")) # I do not see any Auto casting available, the IDE throws an error, cannot assign type Object to type TestClass without forcing the casts, no big deal but I wonder if the Type Cast is the issue and is somehow returning an empty TestClass instance.

Var classOut As Object = Deserialize(dataOut) # Where dataOut is the complete data of the property that is a class.
Var cf As Object = loadObjectType.Field(className) # Where loadObjectType is the parent object Type, className is the field name of the property in the parent object with respect to the child class.
cf.SetValue(loadObject, classOut) # Where loadObject is the parent object, and classOut is the object returned by the Deserialize function
Messagebox("Child | " + classOut.shutdown_code.ToString() + EndOfLine.Native + "Parent | " + loadObject.child.shutdown_code.ToString()) #Results in Child | 25 /n Parent | 25 as expected.

#End of Deserialize function
Return loadObject

Now heading back to our button after deserialize is called

Messagebox(loadtest.child.shutdown_code.ToString()) # NothingReferenceException: Cannot call method 'ToString' because the receiver is Nothing

Messagebox(loadtest.MyInteger.ToString()) #Reports the correct value of MyInteger so the loadtest/loadObject are at least partially intact

I can share more code or even the project file if its easier to figure this out, I am probably doing something wrong but I am so lost lol, loadObject and classOut are both intact but after the return and typecast it dies. I thought this would be an issue with the deserialize function returning an Object but within the scope of the function loadObject is correct it is only once it is returned things go south.

Syntec

Sorry just to clarify this, SEC.Load is a Function that calls SEC.Deserialize however checking the above in SEC.Load yields the same errors, so its not a Return of a Return issue with the SEC.Load function.

Syntec

Further to this (sorry I know, I am debugging in the forum), using TypeInfo to create an instance of the class in SEC.Load and setting it from Deserialize and forcing its Type via Type Casting yields the same results. I am so confused where this is actually occurring because Desererialize is returning a valid child class and setting the parent class child class properly as evident by the classOut / loadObject messagebox calls... so it should also be returning loadObject properly but it isn't 🙁 and my brain hurts.

Syntec

After sleeping on this, the only thing I can think of is that once loadObject is Returned from SEC.Deserialize the classOut drops out of scope and is automatically cleaned up, even though its reference count should still include loadObject. Primitives work as expected because they are pass by value rather than pass by reference. So this might be an error in the way I am doing this.

Further to the above, If I do the following in the deserailize function

Var copyClassOut As New TestConfig
copyClassOut.shutdown_code = classOut.shutdown_code

loadObject.config = copyClassOut

It works, so the issue is for sure scope and cleanup. I can probably do this copyClassOut via additional introspection in the Deserialize function but I am worried what happens with a child class of a child class and wonder if it will drop out of scope on me... will need to do some more testing.

I think the workaround may be for me to pass an object instance into the deserialize function rather than letting it create the instance... that way it should hopefully maintain scope and reference count the way I expect.

Garry

Thanks for the detailed report. This was a genuine bug in Objo, not something you were doing wrong. It's fixed now and will ship with the next release: https://feedback.objo.dev/bug/1086

What was happening

Your deserialisation logic was fine. The problem was in FieldInfo.SetValue: when it stored an object (like your child TestClass) into a parent field, that field never took ownership of the object's memory. Your local variable (classOut) was what kept the child alive, so everything looked correct inside Deserialize — but the moment the function returned and the local went out of scope, the child was destroyed even though the parent still held a reference to it. That's why MyInteger survived (value types aren't reference-counted) while child became Nothing and blew up on .ToString().

The cast wasn't involved either - TestClass(...) is a checked reference cast that keeps the same object, so loadTest really was your deserialised parent. The child was simply already gone by the time you read it.

What's fixed

FieldInfo.SetValue now retains object references properly, so nested objects (and arrays and dictionaries) stay alive as long as a field points at them. Object graphs survive across function boundaries.
Overwriting an object-valued field now releases the previous value instead of leaking it.
Setting a field to its own current value is now safe.
Shared fields (FieldInfo.IsShared) now work correctly with SetValue/GetValue — previously they weren't handled properly at all.
SetValue now validates its arguments: the target must be an instance of the field's declaring type (or a subtype), and the value must match the field's declared type, otherwise you get a clear runtime error. Nothing is accepted for reference-typed fields but rejected for value types like Integer and String.

Until you update

If you want the fix straight away, the ARC-safe paths that already worked correctly are PropertyInfo.SetValue and the global SetProperty:

# Instead of FieldInfo.SetValue
Var p As Object = loadObjectType.Property(className)  # PropertyInfo
p.SetValue(loadObject, classOut)

# or the global convenience function
SetProperty(loadObject, className, classOut)

Both route through the same safe path as ordinary property assignment.

Syntec

Garry Thank you Garry, everything is working perfectly now!

Garry

Wonderful!