Hey guys, using Gson, I made a generic method that...

# announcements

[Ofir Bar]

Hey guys, using Gson, I made a generic method that performs a deep copy on an object.

inline fun<reified T> Any.deepCopy(): T {
    val JSON = Gson().toJson(this)
    return Gson().fromJson(JSON, T::class.java)
}

However, when I try to perform this Deep Copy on a List, the items on the list are LinkedTreeMap .
Can anyone correct me as what can I possible do to resolve it?

[David Eriksson]

Are you sure that you call deepCopy with T=ArrayList<Applicant> and not with T=Any?

[jw]

Please never use Gson. Signed, one of its maintainers.

[Ofir Bar]

Lol, too late my friend @jw

[Ofir Bar]

Hmm, I am not sure @David Eriksson
How can I debug this?
Breakpoints on a generic function doesn't seem to allow me intercepting type T.

Anyway, I just found this SO article - https://stackoverflow.com/questions/32444863/google-gson-linkedtreemap-class-cast-to-myclass

Seems that there might be something with Java Type erasure.
Not sure what that is, I will research

[David Eriksson]

Just breakppint in fromJson and examine the clazz

[Ofir Bar]

@David Eriksson
Yes, when debugging "this" I get T = ArrayList<Applicant>:

[bezrukov]

I would try to use TypeToken instead of T::class.java

[bezrukov]

so it will be

return Gson().fromJson(JSON, object : TypeToken<T>() {}.type)

[bezrukov]

but it should work without it too, are you sure you're calling it as
someObject.deepCopy<ArrayList<Applicant>>?
this ref isn't what David asked, he asked you to enter into fromJson method, and examine what is passed as T::class.java

[bezrukov]

I would suggest changing Any -> T in signature, then type inference know what is T without writing it in <>

[Ofir Bar]

@bezrukov
Ohh, here is T::class.java , something seems not right
Sorry if I seem confused, I am a junior dev

As for the TypeToken, it works perfectly, thank you! I just need to research and understand why hahaha

[jw]

It's because T::class.java is ArrayList.class and there's no type information for the contained items. You can use typeOf<T> to get a KType and then get a Type from that