A PreviousState Resource, accessible in OnEnter

[ChristopherBiscardi]

What problem does this solve or what need does it fill?

There is State and NextState, but no PreviousState. This means to handle transitions you have to pre-specify all state transition variants at the type level with OnTransition{ exited: AppState::Previous, entered: AppState::Other }.

It would be useful if system in OnEnter could access the state that was recently exited or if OnTransition could support the root AppState instead of a specific variant.

What solution would you like?

Options:

1. A readable PreviousState resource, similar to State and NextState.
2. An OnTransition variant that can match any/all variants of a state.

What alternative(s) have you considered?

• Specifying all transitions at the type level in separate.
• Making the Resource that holds previous state in userland

Additional context

This feature was asked for by Calin, I am filing it for them after asking about their usecase since they don't have gh access at the moment.

my use-case here specifically is making a Gamestate variant, Refresh, which takes the PreviousState and uses it to determine what should happen (in a system that handles state refreshes).

• Calin

[alice-i-cecile]

This is a nice idea, and shouldn't be too expensive. I like this idea!