This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of C++14 status.

2210. Missing allocator-extended constructor for allocator-aware containers

Section: 24.3 [sequences], 24.4 [associative], 24.5 [unord] Status: C++14 Submitter: Jonathan Wakely Opened: 2012-11-01 Last modified: 2016-01-28

Priority: Not Prioritized

View all other issues in [sequences].

View all issues with C++14 status.

Discussion:

The forward_list(size_type) constructor has no allocator-extended equivalent, preventing the following code from compiling:

#include <forward_list>
#include <vector>
#include <scoped_allocator>

using namespace std;

int main()
{
  using list = forward_list<int>;
  vector<list, scoped_allocator_adaptor<list::allocator_type>> v;
  v.emplace_back(1u);
}

The very same problem exists for all allocator-aware sequence containers.

In addition it exists for associative containers. For example, it's possible to construct std::set<int>{0, 1, 2} but not std::set<int>{{0, 1, 2}, alloc}, and possible to construct std::set<int>{begin, end} but not std::set<int>{begin, end, alloc}.

This makes the following program fail when SCOPED is defined:

#include <set>
#include <vector>
#include <scoped_allocator>

#if SCOPED
using A = std::scoped_allocator_adaptor<std::allocator<int>>;
#else
using A = std::allocator<int>;
#endif

int main()
{
  int values[] = {0, 1, 2};
  std::vector<std::set<int>, A> v;
  v.emplace_back(std::begin(values), std::end(values));
}

[2013-03-15 Issues Teleconference]

Moved to Review.

Jonathan: There are lots of places where this is missing.

Howard: We should ping Pablo, this might be a deliberate design decision.

[2013-04-18, Bristol]

Proposed resolution:

This wording is relative to N3485.

1. Edit the synopsis in 24.3.8.1 [deque.overview]/2:

   namespace std {
     template <class T, class Allocator = allocator<T> >
     class deque {
     public:
       […]
       explicit deque(const Allocator& = Allocator());
       explicit deque(size_type n, const Allocator& = Allocator());
       […]
     };
   }
   

2. Edit 24.3.8.2 [deque.cons]/2:

   explicit deque(size_type n, const Allocator& = Allocator());
   

   -3- Effects: Constructs a deque with n default-inserted elements using the specified allocator.

3. Edit the synopsis in [forwardlist.overview]/3:

   namespace std {
     template <class T, class Allocator = allocator<T> >
     class forward_list {
     public:
       […]
       explicit forward_list(const Allocator& = Allocator());
       explicit forward_list(size_type n, const Allocator& = Allocator());
       […]
     };
   }
   

4. Edit [forwardlist.cons]/3:

   explicit forward_list(size_type n, const Allocator& = Allocator());
   

   -3- Effects: Constructs a forward_list object with n default-inserted elements using the specified allocator.

5. Edit the synopsis in 24.3.10.1 [list.overview]/2:

   namespace std {
     template <class T, class Allocator = allocator<T> >
     class list {
     public:
       […]
       explicit list(const Allocator& = Allocator());
       explicit list(size_type n, const Allocator& = Allocator());
       […]
     };
   }
   

6. Edit 24.3.10.2 [list.cons]/3:

   explicit list(size_type n, const Allocator& = Allocator());
   

   -3- Effects: Constructs a list with n default-inserted elements using the specified allocator.

7. Edit the synopsis in 24.3.11.1 [vector.overview]/2:

   namespace std {
     template <class T, class Allocator = allocator<T> >
     class vector {
     public:
       […]
       explicit vector(const Allocator& = Allocator());
       explicit vector(size_type n, const Allocator& = Allocator());
       […]
     };
   }
   

8. Edit 24.3.11.2 [vector.cons]/3:

   explicit vector(size_type n, const Allocator& = Allocator());
   

   -3- Effects: Constructs a vector with n default-inserted elements using the specified allocator.

9. Edit the synopsis in 24.3.12 [vector.bool]/1:

   namespace std {
     template <class Allocator> class vector<bool, Allocator> {
     class vector {
     public:
       […]
       explicit vector(const Allocator& = Allocator());
       explicit vector(size_type n, const Allocator& = Allocator());
       explicit vector(size_type n, const bool& value = bool(),
                       const Allocator& = Allocator());
       […]
     };
   }
   

10. Add to the synopsis in 24.4.4.1 [map.overview] p2:

    namespace std {
      template <class Key, class T, class Compare = less<Key>,
        class Allocator = allocator<pair<const Key, T> > > {
      class map {
      public:
        […]
        map(initializer_list<value_type>,
          const Compare& = Compare(),
          const Allocator& = Allocator());
        template <class InputIterator>
        map(InputIterator first, InputIterator last, const Allocator& a)
          : map(first, last, Compare(), a) { }
        map(initializer_list<value_type> il, const Allocator& a)
          : map(il, Compare(), a) { }
        ~map();
        […]
      };
    }
    

11. Add to the synopsis in 24.4.5.1 [multimap.overview] p2:

    namespace std {
      template <class Key, class T, class Compare = less<Key>,
        class Allocator = allocator<pair<const Key, T> > > {
      class multimap {
      public:
        […]
        multimap(initializer_list<value_type>,
          const Compare& = Compare(),
          const Allocator& = Allocator());
        template <class InputIterator>
        multimap(InputIterator first, InputIterator last, const Allocator& a)
          : multimap(first, last, Compare(), a) { }
        multimap(initializer_list<value_type> il, const Allocator& a)
          : multimap(il, Compare(), a) { }
        ~multimap();
        […]
      };
    }
    

12. Add to the synopsis in 24.4.6.1 [set.overview] p2:

    namespace std {
      template <class Key, class Compare = less<Key>,
        class Allocator = allocator<Key> > {
      class set {
      public:
        […]
        set(initializer_list<value_type>,
          const Compare& = Compare(),
          const Allocator& = Allocator());
        template <class InputIterator>
        set(InputIterator first, InputIterator last, const Allocator& a)
          : set(first, last, Compare(), a) { }
        set(initializer_list<value_type> il, const Allocator& a)
          : set(il, Compare(), a) { }
        ~set();
        […]
      };
    }
    

13. Add to the synopsis in 24.4.7.1 [multiset.overview] p2:

    namespace std {
      template <class Key, class Compare = less<Key>,
        class Allocator = allocator<Key> > {
      class multiset {
      public:
        […]
        multiset(initializer_list<value_type>,
          const Compare& = Compare(),
          const Allocator& = Allocator());
        template <class InputIterator>
        multiset(InputIterator first, InputIterator last, const Allocator& a)
          : multiset(first, last, Compare(), a) { }
        multiset(initializer_list<value_type> il, const Allocator& a)
          : multiset(il, Compare(), a) { }
        ~multiset();
        […]
      };
    }
    

14. Add to the synopsis in 24.5.4.1 [unord.map.overview] p3:

    namespace std {
      template <class Key, class T,
        class Hash = hash<Key>,
        class Pred = std::equal_to<Key>,
        class Allocator = std::allocator<std::pair<const Key, T> > > {
      class unordered_map {
      public:
        […]
        unordered_map(initializer_list<value_type>,
          size_type = see below,
          const hasher& hf = hasher(),
          const key_equal& eql = key_equal(),
          const allocator_type& a = allocator_type());
        unordered_map(size_type n, const allocator_type& a)
          : unordered_map(n, hasher(), key_equal(), a) { }
        unordered_map(size_type n, const hasher& hf, const allocator_type& a)
          : unordered_map(n, hf, key_equal(), a) { }
        template <class InputIterator>
          unordered_map(InputIterator f, InputIterator l, size_type n, const allocator_type& a)
          : unordered_map(f, l, n, hasher(), key_equal(), a) { }
        template <class InputIterator>
          unordered_map(InputIterator f, InputIterator l, size_type n, const hasher& hf, 
    	    const allocator_type& a)
          : unordered_map(f, l, n, hf, key_equal(), a) { }
        unordered_map(initializer_list<value_type> il, size_type n, const allocator_type& a)
          : unordered_map(il, n, hasher(), key_equal(), a) { }
        unordered_map(initializer_list<value_type> il, size_type n, const hasher& hf, 
    	  const allocator_type& a)
          : unordered_map(il, n, hf, key_equal(), a) { }
        ~unordered_map();
        […]
      };
    }
    

15. Add to the synopsis in 24.5.5.1 [unord.multimap.overview] p3:

    namespace std {
      template <class Key, class T,
        class Hash = hash<Key>,
        class Pred = std::equal_to<Key>,
        class Allocator = std::allocator<std::pair<const Key, T> > > {
      class unordered_multimap {
      public:
        […]
        unordered_multimap(initializer_list<value_type>,
          size_type = see below,
          const hasher& hf = hasher(),
          const key_equal& eql = key_equal(),
          const allocator_type& a = allocator_type());
        unordered_multimap(size_type n, const allocator_type& a)
          : unordered_multimap(n, hasher(), key_equal(), a) { }
        unordered_multimap(size_type n, const hasher& hf, const allocator_type& a)
          : unordered_multimap(n, hf, key_equal(), a) { }
        template <class InputIterator>
          unordered_multimap(InputIterator f, InputIterator l, size_type n, const allocator_type& a)
          : unordered_multimap(f, l, n, hasher(), key_equal(), a) { }
        template <class InputIterator>
          unordered_multimap(InputIterator f, InputIterator l, size_type n, const hasher& hf, 
    	    const allocator_type& a)
          : unordered_multimap(f, l, n, hf, key_equal(), a) { }
        unordered_multimap(initializer_list<value_type> il, size_type n, const allocator_type& a)
          : unordered_multimap(il, n, hasher(), key_equal(), a) { }
        unordered_multimap(initializer_list<value_type> il, size_type n, const hasher& hf, 
    	  const allocator_type& a)
          : unordered_multimap(il, n, hf, key_equal(), a) { }
        ~unordered_multimap();
        […]
      };
    }
    

16. Add to the synopsis in 24.5.6.1 [unord.set.overview] p3:

    namespace std {
      template <class Key,
        class Hash = hash<Key>,
        class Pred = std::equal_to<Key>,
        class Allocator = std::allocator<Key> > {
      class unordered_set {
      public:
        […]
        unordered_set(initializer_list<value_type>,
          size_type = see below,
          const hasher& hf = hasher(),
          const key_equal& eql = key_equal(),
          const allocator_type& a = allocator_type());
        unordered_set(size_type n, const allocator_type& a)
          : unordered_set(n, hasher(), key_equal(), a) { }
        unordered_set(size_type n, const hasher& hf, const allocator_type& a)
          : unordered_set(n, hf, key_equal(), a) { }
        template <class InputIterator>
          unordered_set(InputIterator f, InputIterator l, size_type n, const allocator_type& a)
          : unordered_set(f, l, n, hasher(), key_equal(), a) { }
        template <class InputIterator>
          unordered_set(InputIterator f, InputIterator l, size_type n, const hasher& hf, 
    	    const allocator_type& a)
          : unordered_set(f, l, n, hf, key_equal(), a) { }
        unordered_set(initializer_list<value_type> il, size_type n, const allocator_type& a)
          : unordered_set(il, n, hasher(), key_equal(), a) { }
        unordered_set(initializer_list<value_type> il, size_type n, const hasher& hf, 
    	  const allocator_type& a)
          : unordered_set(il, n, hf, key_equal(), a) { }
        ~unordered_set();
        […]
      };
    }
    

17. Add to the synopsis in 24.5.7.1 [unord.multiset.overview] p3:

    namespace std {
      template <class Key,
        class Hash = hash<Key>,
        class Pred = std::equal_to<Key>,
        class Allocator = std::allocator<Key> > {
      class unordered_multiset {
      public:
        […]
        unordered_multiset(initializer_list<value_type>,
          size_type = see below,
          const hasher& hf = hasher(),
          const key_equal& eql = key_equal(),
          const allocator_type& a = allocator_type());
        unordered_multiset(size_type n, const allocator_type& a)
          : unordered_multiset(n, hasher(), key_equal(), a) { }
        unordered_multiset(size_type n, const hasher& hf, const allocator_type& a)
          : unordered_multiset(n, hf, key_equal(), a) { }
        template <class InputIterator>
          unordered_multiset(InputIterator f, InputIterator l, size_type n, const allocator_type& a)
          : unordered_multiset(f, l, n, hasher(), key_equal(), a) { }
        template <class InputIterator>
          unordered_multiset(InputIterator f, InputIterator l, size_type n, const hasher& hf, 
    	    const allocator_type& a)
          : unordered_multiset(f, l, n, hf, key_equal(), a) { }
        unordered_multiset(initializer_list<value_type> il, size_type n, const allocator_type& a)
          : unordered_multiset(il, n, hasher(), key_equal(), a) { }
        unordered_multiset(initializer_list<value_type> il, size_type n, const hasher& hf, 
    	  const allocator_type& a)
          : unordered_multiset(il, n, hf, key_equal(), a) { }
        ~unordered_multiset();
        […]
      };
    }