How to use TypeToken + generics with Gson in Kotlin

Question

I'm unable to get a List of generic type from a custom class (Turns):

val turnsType = TypeToken<List<Turns>>() {}.type val turns = Gson().fromJson(pref.turns, turnsType) 

it said:

cannot access '<init>' it is 'public /*package*/' in 'TypeToken' 

Answer 1

Create this inline fun:

inline fun <reified T> Gson.fromJson(json: String) = fromJson<T>(json, object: TypeToken<T>() {}.type) 

and then you can call it in this way:

val turns = Gson().fromJson<Turns>(pref.turns) // or val turns: Turns = Gson().fromJson(pref.turns) 

Previous Alternatives:

ALTERNATIVE 1:

val turnsType = object : TypeToken<List<Turns>>() {}.type val turns = Gson().fromJson<List<Turns>>(pref.turns, turnsType) 

You have to put object : and the specific type in fromJson<List<Turns>>

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ALTERNATIVE 2:

As @cypressious mention it can be achieved also in this way:

inline fun <reified T> genericType() = object: TypeToken<T>() {}.type 

use as:

val turnsType = genericType<List<Turns>>()