Re: CoW and reference counting in the STL

typedef map<string, pair<list<string>, set<string>>> T;

T list1;
T list2;

.....
list2 = list1;

Copying the complete list or adding elements might fail during copying, if the expansion of one of the elements fails.
It's hard to predict if the available memory if sufficient for a copy / add operation (in this case) due to memory fragmentation etc.

To make a long story short:

I have the feeling that think that most C++ applications can't handle insufficient memory conditions predictably in every situation. For huge contiguous memory blocks yes.
Or asking the other way round, is there a huge difference to recover from:

list2 = list1;

and

list1["hello"] = element;