Krate#moshiPref - why using typeOf instead of class?

[mikef-dk]

Recently we've done some tracing regarding our app start performance. What we noticed is that the very first time typeOf is invoked it takes a long time (~1 second). While we were able to eliminate those calls in our code base, we were noticing that the Moshi extension for Krate is doing it as well:

@OptIn(ExperimentalStdlibApi::class)
public inline fun <reified T : Any> Krate.moshiPref(
    key: String? = null,
): KeyedKratePropertyProvider<T?> {
    return moshiPrefImpl(key, typeOf<T>().javaType)
}

I'm wondering: Is there any good reason to use typeOf<T>().javaType over T::class.java?

Lastly a screenshot of the trace proving the point that typeOf really takes that long:

[zsmb13]

Unfortunately there is a good reason. typeOf can handle nested types being input as the T type parameter (such as List<String>), while ::class.java would erase that to just the List class with its nested parameter lost.

I go into detail on this in this talk: https://zsmb.co/talks/krate-ft-moshi/

That being said, if there are alternatives to typeOf that preserve full types (or if I'm doing something wrong in the library that's causing it to be this slow) I'd be open to improving this.

[mikef-dk]

Thank you very much for the explanation and the link to your talk - very helpful. As far as I'm aware there is nothing wrong that the library is doing - the first invocation of typeOf just seems to be painfully slow no matter where it happens in the code and I'm not aware of any alternative unfortunately.

[mikef-dk]

@zsmb13 After watching your talk and checking your slides I'm wondering whether it would be an option to bring back the old implementation that you were using before switching to typeOf?

We've compared both implementations and those are the results:

typeOf

makeType