Immutable set-keys in c++0x, where?

I heard in a talk that the keys in C++0x associative containers are no longer mutable. Before, in C++03, they have been mutable, and only the Standard's text sai开发者_运维百科d, that the order or keys must stay the same.

Now, luckily, this is illegal:

std::set<int> ss { 2,5,1,6,8,5,8,0,2,4,9 };
auto it = ss.find(4);
*it = 7;  // 'ERROR: assignment of read-only location'

Where is this change reflected in C++0x? I looked Final Draft, but still see that find() and such returns iterator -- that sounds modifiable. (And why this is and must be I gan guess: containers like map want to allow the value beeing modified. What exacly changed to make the key-part const?)

For your information, 23.2.4/5 in N3290 says:

For set and multiset the value type is the same as the key type. For map and multimap it is equal to pair<const Key, T>. Keys in an associative container are immutable.

and 23.2.4/6 says:

For associative containers where the value type is the same as the key type, both iterator and const_iterator are constant iterators.
...
Note: iterator and const_iterator have identical semantics in this case

Does this quote solve your question?

Basically, iterator and const_iterator are now specified to be the same. That's the lowdown, not the technicalities, of course, but it's perfectly legal for set containers to typedef iterator as const_iterator in C++0x.

For map, of course, then it was a pair<const K, V>, so it never had a problem.