Storage options: selecting where to save app

[saona-raimundo]

The current way to have a persistent app is to implement epi::App and use the feature persistence.
In particular, one must implement the method save.

save uses a default location given by:

• Local Storage on the web
• directories_next::ProjectDirs::data_dir on native.

But there is no way (as far as I can see) to change the default location.

Describe the solution you'd like

I would like to be able to choose where the data is stored.

Describe alternatives you've considered

I propose to exhibit the call to create a dyn epi::Storage, so people could change it.

We could add a method to the epi::App trait

fn storage(&self) -> dyn Storage { ... }

A default implementation is given by the current behaviour.

Additional context

A very simple use case is that I would like to store the app data in a Google drive folder, so I get "persistence" across devices too.

[kkharji]

Interesting use case with google drive. How about persistence over backend server 🤔

[emilk]

Perhaps the path could be an option in NativeSettings ?

[wmte]

Perhaps the path could be an option in NativeSettings ?

I worry this does not address user-selectable paths (ie, a typical File->Save action) which I am trying to unify with the current persistence mechanism.

By exposing FileStorage I was able to save to a chosen path on user interaction. In my application I use the default storage behavior as a kind of 'session-resume', but would like to also have manual save and load as I expect users to generate multiple application states.

[emilk]

Closed by #4423