---
title: Schedule API Cleanup
pull_requests: [19352, 20119]
---

In order to support removing systems from schedules, `Vec`s storing `System`s and
`SystemSet`s have been replaced with `SlotMap`s which allow safely removing nodes and
reusing indices. The maps are respectively keyed by `SystemKey`s and `SystemSetKey`s.

The following signatures were changed:

- `NodeId::System`: Now stores a `SystemKey` instead of a plain `usize`
- `NodeId::Set`: Now stores a `SystemSetKey` instead of a plain `usize`
- `ScheduleBuildPass::collapse_set`: Now takes the type-specific keys. Wrap them back into a `NodeId` if necessary.
- The following functions now return the type-specific keys. Wrap them back into a `NodeId` if necessary.
  - `Schedule::systems`
  - `ScheduleGraph::conflicting_systems`

The following functions were replaced. Those that took or returned `NodeId` now
take or return `SystemKey` or `SystemSetKey`. Wrap/unwrap them as necessary.

- `ScheduleGraph::contains_set`: Use `ScheduleGraph::system_sets` and `SystemSets::contains`.
- `ScheduleGraph::get_set_at`: Use `ScheduleGraph::system_sets` and `SystemSets::get`.
- `ScheduleGraph::set_at`: Use `ScheduleGraph::system_sets` and `SystemSets::index` (`system_sets[key]`).
- `ScheduleGraph::get_set_conditions_at`: Use `ScheduleGraph::system_sets` and `SystemSets::get_conditions`.
- `ScheduleGraph::system_sets`: Use `ScheduleGraph::system_sets` and `SystemSets::iter`.
- `ScheduleGraph::get_system_at`: Use `ScheduleGraph::systems` and `Systems::get`.
- `ScheduleGraph::system_at`: Use `ScheduleGraph::systems` and `Systems::index` (`systems[key]`).
- `ScheduleGraph::systems`: Use `ScheduleGraph::systems` and `Systems::iter`.

The following functions were removed:

- `NodeId::index`: You should match on and use the `SystemKey` and `SystemSetKey` instead.
- `NodeId::cmp`: Use the `PartialOrd` and `Ord` traits instead.
- `ScheduleGraph::set_conditions_at`: If needing to check presence of conditions,
  use `ScheduleGraph::system_sets` and `SystemSets::has_conditions`.
  Otherwise, use `SystemSets::get_conditions`.