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6 commits

Author SHA1 Message Date
JoJoJet
3442a13d2c
Use UnsafeWorldCell to increase code quality for SystemParam (#8174)
# Objective

The type `&World` is currently in an awkward place, since it has two
meanings:
1. Read-only access to the entire world.
2. Interior mutable access to the world; immutable and/or mutable access
to certain portions of world data.

This makes `&World` difficult to reason about, and surprising to see in
function signatures if one does not know about the interior mutable
property.

The type `UnsafeWorldCell` was added in #6404, which is meant to
alleviate this confusion by adding a dedicated type for interior mutable
world access. However, much of the engine still treats `&World` as an
interior mutable-ish type. One of those places is `SystemParam`.

## Solution

Modify `SystemParam::get_param` to accept `UnsafeWorldCell` instead of
`&World`. Simplify the safety invariants, since the `UnsafeWorldCell`
type encapsulates the concept of constrained world access.

---

## Changelog

`SystemParam::get_param` now accepts an `UnsafeWorldCell` instead of
`&World`. This type provides a high-level API for unsafe interior
mutable world access.

## Migration Guide

For manual implementers of `SystemParam`: the function `get_item` now
takes `UnsafeWorldCell` instead of `&World`. To access world data, use:

* `.get_entity()`, which returns an `UnsafeEntityCell` which can be used
to access component data.
* `get_resource()` and its variants, to access resource data.
2023-04-01 15:45:07 +00:00
JoJoJet
2e7b915ba4
Increase type safety and clarity for change detection (#7905) 2023-03-09 17:17:02 +00:00
JoJoJet
a69e6a1207 Implement FromWorld for WorldId (#7726)
# Objective

Allow using `Local<WorldId>` in systems.

## Solution

- Describe the solution used to achieve the objective above.

---

## Changelog

+ `WorldId` now implements the `FromWorld` trait.
2023-02-20 15:02:16 +00:00
Liam Gallagher
64b0f19a65 Implement SystemParam for WorldId (#7741)
# Objective

Fixes #7736

## Solution

Implement the `SystemParam` trait for `WorldId`

## Changelog

- `WorldId` can now be taken as a system parameter and will return the id of the world the system is running in
2023-02-19 03:26:13 +00:00
2ne1ugly
0e9f80e00b Implement SparseSetIndex for WorldId (#7125)
# Objective

- Fixes #7124

## Solution

- Add Hash Derive on `WorldId`
- Add `SparseSetIndex` impl
2023-01-09 21:43:27 +00:00
Daniel McNab
5ba2b9adcf Unique WorldId (#2827)
# Objective

Fixes these issues:
- `WorldId`s currently aren't necessarily unique
    - I want to guarantee that they're unique to safeguard my librarified version of https://github.com/bevyengine/bevy/discussions/2805
    - There probably hasn't been a collision yet, but they could technically collide
- `SystemId` isn't used for anything
  - It's no longer used now that `Locals` are stored within the `System`.
- `bevy_ecs` depends on rand

## Solution

- Instead of randomly generating `WorldId`s, just use an incrementing atomic counter, panicing on overflow.
- Remove `SystemId` 
    - We do need to allow Locals for exclusive systems at some point, but exclusive systems couldn't access their own `SystemId` anyway.
- Now that these don't depend on rand, move it to a dev-dependency

## Todo

Determine if `WorldId` should be `u32` based instead
2021-09-30 20:54:47 +00:00