Re: Assignment operator, templates, double associative container
mscava@gmail.com wrote:
stl_algo.h:1076: error: non-static const member `const std::string
DataMapPair::first', can't use default assignment operator
Here's my code:
typedef std::map< std::string,
std::pair< bool, CountedPtr<T> > >
DataMap;
typedef std::pair< std::string,
std::pair< bool, CountedPtr<T> > >
DataMapPair;
First thing here: you might want to replace the second typedef with
typedef DataMap::element_type DataMapPair;
although, and that might make the difference, maps use a const key as first
type to pair, so it would be a 'pair<string const, pair<...> >'.
DataMap dataMap_;
template <typename T> bool DataManager<T> ::
IsGarbage( const DataMapPair& dmPair )
I think the '<T>' is wrong after DataManager.
template <typename T> void DataManager<T> ::
CollectGarbage()
{
dataMap_.erase( remove_if( dataMap_.begin(), dataMap_.end(),
IsGarbage ), dataMap_.end() );
}
Can anyone tell how should I oveload that operator=? Or should I do
something else?
Okay, take a look at remove_if(). It reorders the elements so that the
non-fitting elements go to the end. However, you can't reorder the content
of a map, as it internally sorts it and needs that order! Hence also the
use of a const key type.
Typical solution:
it = map.begin();
while(it!=map.end())
if( predicate(*it))
map.erase(it++);
else
++it;
Note the use of the postfix increment operator. This works for all
containers where erasing in the middle doesn't invalidate iterators, i.e.
all except deque and vector.
BTW: you could have removed all the template stuff and still have a
complete example, which would have made it much easier to read. Also, you
didn't give any information whatsoever where exactly in the code the error
occurred. Lastly, even if you had given the line, there still would have
been too many statements in that line.
Uli
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