Ryan wrote:
On Thu, Sep 24, 2009 at 12:01 PM, Nat Goodspeed <nat@lindenlab.com> wrote:
Yes, that's what I was thinking: migrate the int from the key to the mapped_type.
This would indeed make the insert easier at the cost of complicating the retrieval. By making the int part of the key the retrieval is trival
m_VariableDestinations.find(std::make_pair(name, intValue));
If I was to move the int out of the pair I found that it increased the difficulty quite a bit.
I don't think it's that bad. The retrieval will be only slightly worse with an extra ".second" you'd need to add to get the vector of classA.
On Thu, Sep 24, 2009 at 11:38 AM, Anthony Foglia <AFoglia@princeton.com>wrote:
He can pass a custom less functor class as the third template parameter to the map. Something like:
Is the advantave of using the custom functor over the lambda class the ability to use the insert function correctly? By using the functor the insert, that Nat recommended, would indeed only compare the name value and correctly return true or false regardless of the second parameter. Is this correct?
Yes, but it also will only compare the string value and not the int when using map::find as well. The only real difference comes down to how you get the vector<classA> value and the intValue from the iter. typedef map< pair<string,int>, vector<classA>, LessFirstOfPair > cMap1; typedef map< string, pair<int,vector<classA> > > cMap2; cMap1 map1; cMap2 map2; cMap1::iterator it1 = map1.find(make_pair(name,intValue)); cMap2::iterator it2 = map2.find(name); The int part of the "key" can be retrieved with it1->first.second it2->second.first And the vector<classA> can be retrieved with it1->second it2->second.second I guess one benefit is that by overriding the template parameter, using std::find_if becomes a little simpler, because both the string and int are in the same "area". I think you can get away with find_if(map1.begin(), map1.end(), bind(&cMap1::value_type::first, _1) ==make_pair(givenName, intValue)); but I haven't used bind and lambda often enough to be more than 60% certain I got that right. :-) Using map::find should be faster for big containers, but you'll need to manually check the int of the map key. it1 = map1.find(make_pair(name,intValue)); if ((it1 == map1.end()) || (it1->first.second != intValue)) { // not found } Using merely the string as the key sounds safer to me, both because it's easier to initially code, and it's easier to maintain. (Eventually you or the next coder will forget that in cMap1 the int part of the key is ignored.) I just kept the overloaded template parameter in my reply because that was my first thought. While writing it I realized the simpler, non-overengineered string-only key approach. -- Anthony Foglia Princeton Consultants (609) 987-8787 x233