Crate moirai 

Moirai is a single-threaded, no_std + alloc entity-component-system library.

The public surface is a set of concept-level namespaces, curated root re-exports, and a smaller system-authoring prelude. Implementation modules such as allocators, registries, storage engines, command queues, and schedule runners stay private.

Crate root and prelude admission

Common application, world, schedule, query, bundle, state, and time vocabulary is available at the crate root. prelude contains the subset normally needed to author systems. Advanced construction helpers such as world::BundleWriter stay in their semantic namespace.

Learn by example

examples is the canonical ordered learning path. Its stable, runnable doctests progress from a first app through scheduling, queries, and deterministic replay.

Privacy boundary

Internal modules are not reachable from downstream crates:

use moirai::entity::allocator;

use moirai::storage;

use moirai::component::registry;

Re-exports

pub use component::ComponentId;

pub use component::ComponentOptions;

pub use component::StorageKind;

pub use event::ComponentAdded;

pub use event::ComponentRemoved;

pub use event::EventId;

pub use event::EventOptions;

pub use event::EventReader;

pub use event::EventReaderStart;

pub use event::EventRegistrationError;

pub use event::EventRetention;

pub use math::Q16;

pub use query::ExactIdPolicy;

pub use query::PreparedQuery1;

pub use query::PreparedQuery2;

pub use query::Query1;

pub use query::Query2;

pub use query::QueryCommands;

pub use query::QueryCursor;

pub use query::QueryEffects;

pub use query::QueryError;

pub use query::QueryPolicy;

pub use query::QuerySpec;

pub use query::QueryWindow;

pub use schedule::stage;

pub use schedule::Condition;

pub use schedule::ConditionError;

pub use schedule::FlushMode;

pub use schedule::Schedule;

pub use schedule::ScheduleBuilder;

pub use schedule::ScheduleError;

pub use schedule::StageId;

pub use schedule::System;

pub use schedule::SystemId;

pub use schedule::SystemInitContext;

pub use schedule::SystemSet;

pub use schedule::UpdatePlan;

pub use state::apply;

pub use state::on_enter;

pub use state::on_exit;

pub use state::on_transition;

pub use state::State;

pub use state::StateError;

pub use world::Bundle;

pub use world::Commands;

pub use world::DenseEntityScratch;

pub use world::DynamicBundle;

pub use world::EntityScratchError;

pub use world::World;

pub use world::WorldBuilder;

pub use world::WorldError;

Modules

component

Component registration, storage policy, and dense registry-local handles.

diagnostics

Platform-neutral diagnostic observer contracts for crate::App execution.

event

Typed event registration, retention policy, and independent readers.

examples

Progressive, runnable lessons for learning Moirai through its public API.

math

Deterministic fixed-point helpers for host-side simulation math.

prelude

System-authoring essentials for Moirai hosts.

query

Query selection, traversal, caching, and safe mutation.

schedule

Deterministic ECS schedule: stages, systems, conditions, and deferred flush policy.

state

Explicit host state machine backed by a crate::world::World resource.

testkit

Deterministic replay, step records, drivers, and report comparison for host tests.

world

ECS World: entities, components, resources, events, and deferred Commands.

Structs

App

Runnable ECS host pairing one World with one compiled Schedule.

AppBuilder

Checked application construction: world seeding, schedule authoring, observer wiring.

AppFault

Terminal execution record retained after the first fault.

ChangeTick

Monotonic world change counter for component/resource mutation metadata.

EntityId

Opaque entity handle relative to one crate::world::World.

FixedConfig

Host-provided fixed timestep: interval, substep cap, and debt policy.

FixedDebtCoalesced

Whole fixed intervals represented by one coalesced FixedUpdate run. Whole fixed intervals combined into one coalesced FixedUpdate run.

FixedDebtDropped

Whole fixed intervals discarded when debt exceeds the substep cap.

FixedStep

Fixed simulation substep identity while FixedUpdate runs.

Revision

A checked monotonic revision counter.

RevisionExhausted

Returned when a Revision cannot advance without overflowing.

RevisionKey

A fixed-width collection of revisions suitable for cache keys.

WorldTick

Monotonic frame counter advanced once per successful Update pass.

Enums

AppError

Recoverable preflight failures and terminal execution faults for App.

BuildError

Schedule construction failure before first execution.

FixedDebtPolicy

Policy used when a frame contains more whole fixed intervals than FixedConfig::max_substeps.

StageOperation

Which crate::App operation owns a stage, frame channel, or structural command surface.