using

Using

This package provides a Releasable mixin to upgrade classes with automatic resource cleanup and finalization features.

Examples

class Resource with Releasable {
  // manage resource

  @override
  void release() {
    // clean-up resource in this method
    // and make sure super.release() is called!
    super.release();
  }
}

void main() {
  Resource? res;
  try {
    res = Resource(); // allocate
    // use resource
  } finally {
    // release in a finally block to ensure resources are released
    // even when an error occurs
    res?.release();
  }
}

Extension methods are provided to support syntaxes similar to C#'s using and Java's try-with-resource. They also help make sure resources are properly released!

void main() {
  final data = Resource().use((res) {
    // use `res` to load and return some data
  });
  // the instance created by `Resource()` is guaranteed to be released

  final asyncData = await Resource().useAsync((res) async {
    // use `res` to load and return some data
  });
  // the instance created by `Resource()` is guaranteed to be released
}

Streams are also supported via the consume() extension method:

void main() {
  final outputs = await Resource().consume(inputStream, (res, input) async {
    // use `res` to process inputs and return outputs
  }).toList();
  // the instance created by `Resource()` is guaranteed to be released
}

Automatic finalization is also available to try ensure resources will be released even in situations where release() has not been called. However, no promises are made that this will really happen. For more information, see Dart's documentation for Finalizer.

class ResourceOwner with Releasable {
  final _res1 = Resource();
  final _res2 = Resource();

  ResourceOwner() {
    // non-deterministic clean-up relying on Dart's `Finalizer` class. If
    // the resource owner goes out of scope and `release()` was not called,
    // the two resources should eventually be released and reclaimed by a
    // `Finalizer`.
    autoRelease([_res1, _res2]);
  }

  // deterministic clean-up by explicitly calling `release()` on this
  // instance, or when the instance is used via extension methods (`use()`,
  // `consume()`...).
  @override
  void release() {
    // clean-up resources
    _res1.release();
    _res2.release();
    // call super method
    super.release();
  }
}