async_zone 0.1.0

Declarative async and error handling for Flutter inspired by React Suspense and Error Boundary. Throw futures during build to suspend the surrounding AsyncZone and show its fallback.

0.1.0

Initial release.

Features

• AsyncZone widget that renders a fallback while descendants are suspended on a pending Future, inspired by React Suspense. Exposes alignment and fit to control the internal Stack layout.
• ZoneWidget and StatefulZoneWidget base classes, plus the inline ZoneBuilder, for using AsyncZone.of(context).use(future) during build.
• AsyncZone.of throws a descriptive FlutterError both when no AsyncZone ancestor exists and when called from an element that does not mix in ZoneElement.
• Identity-based caching: repeated use() calls with the same Future instance return the resolved value without re-suspending, and entries are reclaimed automatically when the future is no longer referenced.
• Pending futures are superseded when the calling element rebuilds with a new future or is unmounted, so stale completions never replace fresh results.
• Sliver-shaped variants SliverZoneWidget, SliverStatefulZoneWidget, and SliverZoneBuilder, plus the SliverZoneElementMixin for composing custom sliver elements with ZoneElement.
• Low-level ErrorZoneWidget / StatefulErrorZoneWidget base classes with React-style getDerivedStateFromError, componentDidCatch, resetErrorBoundary, and showErrorBoundary, plus the ErrorBoundaryMixin and ErrorZoneElement for composing the lifecycle into custom widgets.
• Errors thrown inside an inner error zone's fallback (or by ZoneWidget descendants of that fallback) escalate to the next outer error zone, mirroring React's error boundary semantics.
• TransitionZoneBridge / TransitionZoneProvider bridge interface that lets external coordinators (such as the companion async_transition_boundary package) keep the previous subtree visible while a new state suspends.

Documentation

• Bilingual README (English / Japanese), architecture overview, and dartdoc with runnable examples for every public API.