id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
11993,Add a default constructor to intrusive unordered_set and unordered_multiset,anonymous,Ion Gaztañaga,"All the constructors of intrusive `unordered_set` and `unordered_multiset` require a `bucket_traits`. It is currently not possible to instantiate an `unordered_set` without having allocated some buckets.

It would be useful to add a default constructor to `unordered_set` and `unordered_multiset`. That would allow to create hash containers that allocate buckets lazily at the first element insertion.

That would also allow this kind of pattern:
{{{#!c++
unordered_set<MyType, ...> v;
if (some_condition) {
  v = some_collection();
} else {
  v = some_other_collection();
}
}}}

Bonus if the const methods of a default-constructed unordered_set/unordered_multiset can be called and behave as an empty collection (in particular `empty`, `size`, `begin`/`cbegin`, `end`/`cend`, `count`, `find` and `equal_range`).",Feature Requests,closed,To Be Determined,intrusive,Boost 1.60.0,Problem,wontfix,,