bevyengine
Get `ResMut` of a resource from `World`
I can change it so World::resource_mut returns ResMut instead of Mut as well if that's desired, but that could also be added later in a seperate pr.
Let's keep this split this out.
Originally posted by @alice-i-cecile in https://github.com/bevyengine/bevy/issues/11561#issuecomment-1913222497
What problem does this solve or what need does it fill?
There should be a way to get change-detection-enabled, mutable access to a resource from the World. The type that's conventionally used for that is ResMut
What solution would you like?
Add a method to World that supports that / change the current implementation of resource_mut (and the like) to get ResMut instead of Mut and/or &mut T
What alternative(s) have you considered?
Keep as is
What's the reason for needing both Mut & ResMut? Both are exclusive refs + change tracking, the difference between them is just that ResMut is a system param. There's also an From<ResMut> for Mut.
What's the reason for needing both
Mut&ResMut?
ResMut<T> requires that T implements Resource whereas Mut<T> does not. Since the methods mentioned above are only concerned with Resources introducing this additional bound to them/their return types is sensible.
The issue proposed two alternatives, the former being adding a new method, which I was curious about. I agree with the second one of changing the existing functions :)
We've always treated Mut<T> is bevy's primtive for change detection. The only reason that ResMut exists is because SystemParams don't have methods, so you need to use the type to specify that you are requesting a resource via the type. There's no other reason to use a ResMut instead of a Mut, so we should use them in as few places as possible. We already do this, see how ResMut::map_unchanged and ResMut::reborrow return Mut.
Thank you for the issue, but I'm going to close this since we're likely going to move in the direction described in #11825