Lewis Hyatt wrote:
* provide an easy way to sort lists of pointers (without having to make a custom '<' operator each time).
this is already in boost:
some_iterator begin, end; std::sort(boost::indirect_iterator(begin), boost::indirect_iterator(end));
nice, didn't know that one :)
* Easy way to specify different
comparison operators for various subfields. ie. in stead of one complex '<' operator, specify one for each subfield and then define sortorder (which subfield first, ...) on sorttime.
This is an intriguing possibility, what about some intrusive design, where you can tag class members as sort keys?
I'm fine with intrusive, but actually i would prefer an adapter class. something like (simplified interface for readability): template<typename SourceClass,typename FieldType1,typename fieldType2, ...> class sort_field_adapter { const FieldType1& extractField1(const SourceClass& source); const FieldType1& extractField2(const SourceClass& source); ... }; rationale: This could be used to create sort keys "on the fly" (for example, sort by sum of member a+b). I am not sure if it is possible to define an easy, generic adapter interface due to the unknown number and types of the fields.
* provide a good set of default '<' operators. at least: - simple types (strings, numbers, ...) - pointers to simple types - pairs of the above
Simple types and pairs already have operator<, and pointers are handled by indirect_iterator.
is it possible to use indirect_iterator (or similar) if only one half of a pair is a pointer ?
* Specify ascending vs. descending sorting. Trivial criteria really, but reduces complexity (or number) of the '<' operators.
std::sort(begin, end, std::greater<type>());
ofc, but what about your custom < operators, functors. You would need to supply a second, inverted version. Michael