Joaquin M Lopez Munoz skrev:
The situation is characterized by the need to calculate the key after the mapped value (a heavy object) has been placed in the pair. To calculate the key the mapped value needs to be modified (the key is calculated as a side-effect).
I therefore suggest that we add a new function:
typedef ... map; map m; map::node_ptr p = m.get_node_ptr(<like emplace, but only for constructing the mapped value>); p->pair.first = modify( p->pair.second ); m.insert( boost::move(p) );
Thoughts?
Why can't you just do the following?
map::mapped_type x=...; map::key_type k=modify(x); m.emplace(boost::move(k),boost::move(x));
I could, but moving the mapped object is just as expensive as copy-construction, and it is exactly this I want to avoid. -Thorsten