what do you guys think about code like this is this kosher

Question

trevjones · Answer

all of those `doOn` calls are side effects which announce the status of the download The single abstraction already provides you with `downloading` when it is non terminal and `failed` when the single terminates with onError `idle` is the absence of a single being executed also chatRepository seems like an odd place to track attachment download status the name suggests that it houses chats not manages stateful interactions for media downloads is it named properly or is it doing too much

trevjones · Answer

give this a watch <https youtu be 0IKHxjkgop4>

ursus · Answer

Yea its not my code its from a blog post and I also feel weird about it but then philosophically what is a sideffect

ursus · Answer

why is logging okay for sideffecting while writing to a database isnt its same thing just different target console output vs db file

trevjones · Answer

console output doesn t dictate the forward behavior of the application

trevjones · Answer

the DB is state you care about the logs are not

trevjones · Answer

the video goes into some of that

trevjones · Answer

the philosophy of things anyway

ursus · Answer

hmm okay ill give you that

ursus · Answer

so by your definition sideffects are end actions on whose results nobody depends on

ursus · Answer

althought one could argue that writing a Completable to the database is sideffecting since it the end no more transformations technically callsites depends on some query observable of that repository

trevjones · Answer

yea I think that is what I said probably not the right way to describe it I was more trying to say that when I find myself using any of the `doOn` functions for something other than logging I like to stop and ask myself if there is a better way for me to model this into the data type in your case the return type is a single so it isn t bad

trevjones · Answer

but you could make it an observable of some sealed class type that represents all those conditions as well as actively reports file transfer progress and push all of the `chatRepo doStuff` into the ` subscribe` and hopefully contain all of your state mutation signaling to main thread which can really help with keeping behavior predictable

ursus · Answer

well im more investigating what is the definition of sideffect i e what does belong to doOn becasue when you think about it its just some unrelated action a side thing

ursus · Answer

but you could also share the observable subscribe to it once for the db writes second time for the logging

ursus · Answer

so is sideffect just convenience api

trevjones · Answer

shrug <https softwareengineering stackexchange com a 40314>

trevjones · Answer

my thought is this side effect imply s some sort of mutability mutability can make things hard to manage as a system grows as a result I try to represent mutability as an observable of an immutable so that changes always get dispatched appropriately

ursus · Answer

true but writing to a db is a mutating

pg · Answer

This therm isn t rx related to be honest U can read about functional programming to learn what is side effect and what it can cause I think

ursus · Answer

well it originates from functional but rx for sure uses the term its even sometimes in the name functional reactive programming

pg · Answer

FRP represents an intersection of two programming paradigms

ursus · Answer

so

pg · Answer

I just suggest you not be confused by reactive programming vs functional reactive programming nothing else Cheers