Please explain me the difference between `+memo`, `+state`, `+model` and when to use which one ? I ...

# compose

[amar_1995]

Please explain me the difference between +memo, +state, +model and when to use which one ?
I know all of this observing some value and try to recompose on value changes.

[Yann Badoual]

state and model are using memo , they're just convenience wrappers

[Yann Badoual]

fun <T> state( init: () -> T) =     memo { State(init()) }

[Yann Badoual]

fun <T> model(init: () -> T) = memo { init() }

[Yann Badoual]

And The State class is an @Model class meant to wrap around a single value

[Yann Badoual]

So if you just want to cache a single value, you can use state , if you have multiple values and grouping them makes sense, you can use model for that (with a @Model annotated class).

[amar_1995]

And what is the difference in +memo and +model

[Yann Badoual]

From the implementation above none it seems, it's just an alias

[Yann Badoual]

Or maybe the compiler is doing something different with model calls

[amar_1995]

Okay

[amar_1995]

Can you explain me +stateFor take multiple value and so how to access that values and change it.
Let say I use this +stateFor<V1,V2> { something }
As per of doc It says An effect to introduce a state value of type T into a composition that will last as long as the inputs v1 and v2 do not change.
So how to acccess this values and change it accordingly.

[Yann Badoual]

Let's say you have a userCounter state, eg:
val userCounter = +state { 0 }

and everytime you press a button, you'll increment this value, and a textfield will get updated somewhere.

Now let's say that the user can change, and if that's the case, the counter should reset to 0.

You could do something like

val userCounter = +stateFor(userId) { 0 }

With this, when userId changes, the counter will reset.

This example is a bit simplified, and could be replaced by adding a counter property in a User model instead

[Yann Badoual]

(I highly recommend that you read this awesome article http://intelligiblebabble.com/compose-from-first-principles/ , it explains in a simplified way what memo actually does)