ecs-systems

Systems own behavior and state mutation.

Structure

• Resolve dependencies with [Dependency].
• Subscribe in Initialize().
• Keep On... handlers thin.
• Route reusable actions through Try....
• Put checks in Can... without mutation.
• Keep execution in one mutation path.
• Use existing system APIs before resolving lower-level managers.

Entity access

Use TryComp for guard clauses, Resolve when a method accepts Entity<T?>, and EnsureComp for idempotent creation. Prefer EntityQueryEnumerator or established queries over repeated global searches.

Use deferred deletion in handlers or enumeration when immediate deletion could invalidate iteration.

Lifecycle

Account for component startup, shutdown, map initialization, entity deletion, and predicted re-entry. Unsubscribe external callbacks and clean up overlays, timers, or cached references.

Performance

Avoid allocations, LINQ, repeated prototype lookups, and broad queries in Update() or frequent events. Measure before redesigning a hot path.