AsyncMemoizer<T> class Null safety

A class for running an asynchronous function exactly once and caching its result.

An AsyncMemoizer is used when some function may be run multiple times in order to get its result, but it only actually needs to be run once for its effect. To memoize the result of an async function, you can create a memoizer outside the function (for example as an instance field if you want to memoize the result of a method), and then wrap the function's body in a call to runOnce.

This is useful for methods like close() and getters that need to do asynchronous work. For example:

class SomeResource {
  final _closeMemo = AsyncMemoizer();

  Future close() => _closeMemo.runOnce(() {
    // ...
  });
}