std.collection - changing the collection while iterating

[philippecp via Digitalmars-d]

On Sunday, 21 June 2015 at 23:02:38 UTC, Andrei Alexandrescu 
wrote:
> While I work on making std.allocator better, here's some food 
> for thought regarding std.collection.
>
> Consider a traditional container with reference semantics, 
> Java-style. Regarding changing the collection (e.g. 
> adding/removing elements) while iterating, we have the 
> following possibilities:
>
> 1. Leave it undefined, like the STL does. Probably this is too 
> extreme.
>
> 2. Throw an exception if a remove is attempted while ranges 
> exist. This works but it's conservative - e.g. it throws even 
> if those ranges are never to be used again etc.
>
> 3. Allow the removal but throw from the ranges if there's any 
> attempt to use a range following a remove.
>
> 4. Make it work such that ranges continue to be valid post 
> removal. Perhaps this is on the inefficient side.
>
>
> Andrei

I think the best approach is the following:
* Throw exceptions on debug (usability)
* Leave undefined on release (performance)
* Implement another set of collections in 
std.collections.persistent that allows modification of ranges 
without invalidating original range (or changing, aka supports 
snapshotting)that could be referenced somewhere else including 
another thread. Modifications would return a new reference rather 
than be done in place and collections in this namespace are 
immutable.