Hello. David Walthall wrote:

Flex Ferrum wrote:

...

map<int,int> m; vector<int> a,b; std::transform(a.begin(), a.end(), std::back_inserter(b), var(m)[_1]);

Is this a case where transform is not appropriate? My understanding is that the operation supplied to transform must not have any side effects, and here m may be modified by operator[]. Does this count as a side effect?

Yes, of course, map::operator[] _can_ have side effects. But if author of such code absolutely sure what each value from source vector has corresponded map entry then map::operator[] will not have side effects and will suitable for transormation operation. ____________ Best Regards Flex