Don't modify entity objects directly

Seems like that could mean quite a bit more memory right?

Yes, but only for a short time during indexing, before the memory is reclaimed.
This revised patch even improves that by immediately unsetting all cloned items when they aren't needed anymore.

Tested patch from #2 and it looks good to me (although I haven't done any memory usage comparisons)

OK, committed.

I'm not sure this is really working well, I just had an issue with the hierarchy data alteration callback.
I added a property to an entity which is more or less a copy of a taxonomy reference field, I had a problem in the getter callback because when I was trying to access the altered field the structure expected normally looks like the following :
$entity->field_name[LANGUAGE_NONE][0]['tid']
Instead of that, I had sthg like :
$entity->field_name = array( TID_VALUE => TID_VALUE .
To avoid that in my getter callback I load the entity again (unaltered) instead of the entity coming from the parameters of the getter callback.
I don't know if I'm clear enough ! Feel free to ask questions

So you say this doesn't work with a custom property you added?
Did it work before the patch? Otherwise, please create a new issue.
Also, did you define a setter callback that stores the values in the proper format? Maybe that's the problem?

This issue has not seen activity in over 2,5 years. I am therefore closing this issue to clean up the issue queue. Feel free to re-open and update this issue if you feel this issue is still relevant and of importance.