[Boost-users] unordered_map has no lower_bound?

From: Martin Wartens (martin.wartens_at_[hidden])
Date: 2005-03-28 10:39:03

Hi,
I am already using the unordered_map implementation from the file vault. I have 
got some problems with unordered_map, because it offers no "lower_bound" (it is 
not a problem of the implementation, it is simply not in the specs). My 
question is, why is that so and what can I do about it?
The use case is an efficient insert when I have to take special actions when 
the key is already in the container. For a map this would work like:
iter = lower_bound(key); which gets the first element greater or equal to key
Now I can check if the key is already in the map and execute some action to 
handle this case.
Then I can insert the new element in the map with the "hint"-version of insert:
mymap.insert(iter, newelement);
The hint-version starts searching at the hint for the correct insertion point, 
so we don't have to search through the map twice. It is strange that such a 
hint-insert also exists for the unordered_map. But what hint could I give it, 
if I don't have lower_bound?
Thanks,
Martin

PS: there is a small problem in hash_table.hpp causing a warning in VC7.1
line 278 should be:
return (*prev_ptr)!=0;
instead of
return *prev_ptr;