<https://blog.simon-wirtz.de/kotlin-reified-types/...

# feed

[nfrankel]

https://blog.simon-wirtz.de/kotlin-reified-types/

[trubesv]

Funny, I read this this morning in the subway K
Helped me understand and write this dirty line:
inline fun <reified T> getList(json: String): T? = Gson().fromJson<T>(json, object : TypeToken<T>() {}.type)
(used to deserialize an ArrayList of custom objects)

[kevinmost]

is getList the name you want for that method? val user = getList<User>(json) doesn't seem right to me

[kevinmost]

you might also want to have a cached instance of Gson so you're not making new ones for every deserialization

[trubesv]

Actually I use it directly as a parameter so it looks like:

fun newList() { /* create & populate a new list */ }
fun someFunction(list: ArrayList<SomeObject>) { ... }

someFunction(getList(json) ?: newList())

I don't clearly understand exactly why but I don't need to specify <ArrayList<SomeObject>> before the parenthesis somehow

[trubesv]

Also, thanks for noticing the Gson() "error", I must have kept it after trying things and forgot to change it 🙂

[diesieben07]

You don't need to specify the type, because the compiler can infer it.

[trubesv]

Infer it meaning it determines it by "reading" the type of the function parameter?

[diesieben07]

You could put it like that, yes.

[trubesv]

Well, thanks for your input and explanations, it appreciated 🙂

[arthur]

Thanks for this. I didn't know you could do this with reified generics

[trubesv]

@kevinmost Fixed the line to inline fun <reified T> Gson.getList(json: String): T? = fromJson<T>(json, object : TypeToken<T>() {}.type)

[kirillrakhman]

You could also think about caching the type token

[trubesv]

Is this possible in a file where I grouped extensions? (no classes)

[diesieben07]

You can use reified type parameters on any inline function, extension or not.

[trubesv]

@diesieben07 I was asking about caching TypeToken, my guess is that I should val it but does it work outside a class ?

[diesieben07]

You can't really cache the TypeToken, since you don't have anything to cache by (i.e. you don't have a key for the cache).

[trubesv]

Ok I see now, thanks for the explanation 🙂