How can i hold a function with signature `Flow<T> -> U` in a hashmap ? (As the value - key ...

# flow

[asad.awadia]

How can i hold a function with signature Flow<T> -> U in a hashmap ? (As the value - key can be string/int)

[bezrukov]

smth like this

val map = HashMap<String, (Flow<Int>) -> Unit>()

and then

map["test"] = { flow -> Unit }

[asad.awadia]

Not int and unit though - it can be any type..

[Kevin Worth]

Does this work?

val map = HashMap<String, (Flow<Any>) -> Unit>()

[asad.awadia]

Yes it does

But i need the type around so that i can decode a json string to that type (T - which can be anything) and then invoke the handler with that type

[Kevin Worth]

Have you looked into the out keyword? I’m not super strong with it, but perhaps it could help… https://kotlinlang.org/docs/generics.html#declaration-site-variance (may need to scroll up as the docs just above that have quite a bit of context/introduction)

[asad.awadia]

Yes - not sure if it will help
I will go through the doc again thanks

[bezrukov]

can you elaborate your usecase? It's impossible to just declare T (it's not a flow problem, you can't also declare a val property: T). It's impossible to parametrize a property, usually you parametrize either class or function. If you did that - you will be able to just declare it with T (and U instead of Unit).
Otherwise you have to write val map = HashMap<String, (Flow<Any>) -> Any>() as mentioned above and do an unchecked cast

[asad.awadia]

Yes you are right. It is not really a flow problem

I want to hold a list of handlers that can take in user defined input types (could be string or int or a class)

Then at some later point i want to take input from somewhere else, convert it to the right type as expected by the handler and then invoke that handler

So if 1 handler was string and 1 was double - and at some later point i get input 88 - i will invoke the first handler with "88" and the other with 88.0

[asad.awadia]

@bezrukov any idea?