Question

Sometimes it is useful to enumerate a list while it is changing.

e.g.

foreach (var item in listOfEntities)
  item.Update();

// somewhere else (with someEntity contained in listOfEntities)
// an add or remove is made:
someEntity.OnUpdate += (s,e) => listOfEntities.Remove(someEntity);

This will fail if listOfEntities is a List<T>.

There are workarounds like making a copy or a simple for-loop, each with different drawbacks, but I would like to know if there is a list type in the framework (or open source) that supports this.

Answer 1

Look at the collections in System.Collections.Concurrent. There’s no list there, but the collections’ enumerators do “represents a moment-in-time snapshot of the contents of the [collection]”.

These collections are designed for access from multiple threads, so they will be better suited to applications like the code sample you posted.