How can I pass around state without copying an entire structure per message? - elm

Question

I have a textbox that's extremely slow when displaying characters.
I once observed a Stackoverflow exception related to it.
I believe that the performance issue is associated to preparing the portal value:
Sources.InputAccessId _ ->
( { model | portal = portal }, sourceCmd )
Each time a character is keyed-in, I copy and modify a new portal record which consumes more memory.
The code can be found below.
Main:
onSourcesUpdated : Sources.Msg -> Model -> ( Model, Cmd Msg )
onSourcesUpdated subMsg model =
let
pendingPortal =
model.portal
provider =
pendingPortal.provider
profile =
provider.profile
source =
pendingPortal.newSource
( sources, subCmd ) =
Sources.update subMsg
{ profileId = profile.id
, platforms = model.platforms
, source = { source | profileId = profile.id }
, sources = profile.sources
}
sourceCmd =
Cmd.map SourcesUpdated subCmd
pendingProvider =
{ provider | profile = { profile | sources = sources.sources } }
portal =
{ pendingPortal | newSource = sources.source, provider = pendingProvider }
in
case subMsg of
Sources.InputAccessId _ ->
( { model | portal = portal }, sourceCmd )
...
Sources.elm:
update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
let
source =
model.source
in
case msg of
InputAccessId v ->
( { model | source = { source | accessId = v } }, Cmd.none )
...
How can I pass around state without copying entire structures each time an event occurs?

Answer 1

You might want to debounce these events with libraries like this one: elm-debounce
The consequence of debouncing though is that some events will be discarded so you only get one that sums them all when the user is done typing/interacting with the page (more precisely, after a – configurable - timeout).