[Boost-bugs] [Boost C++ Libraries] #11993: Add a default constructor to intrusive unordered_set and unordered_multiset

Subject: [Boost-bugs] [Boost C++ Libraries] #11993: Add a default constructor to intrusive unordered_set and unordered_multiset
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2016-02-17 03:27:13

#11993: Add a default constructor to intrusive unordered_set and unordered_multiset
------------------------------+------------------------
 Reporter:  anonymous         |      Owner:  igaztanaga
     Type:  Feature Requests  |     Status:  new
Milestone:  To Be Determined  |  Component:  intrusive
  Version:  Boost 1.60.0      |   Severity:  Problem
 Keywords:                    |
------------------------------+------------------------
 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`).

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/11993>
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