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Update the implementation details.

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[SVN r47403]
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Daniel James
2008-07-13 20:07:45 +00:00
parent c7bde21be7
commit c49dbd782d
1 changed files with 15 additions and 22 deletions
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doc/rationale.qbk
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@ -96,6 +96,17 @@ efficiency advantage of power of 2 hash tables.
So, this implementation uses a prime number for the hash table size.
[h2 Equality operators and hash functions]
`operator==` and `operator!=` are not included in the standard, but I've
added them as I think they could be useful and can be efficiently
implemented. They are specified
differently to the standard associative containers, comparing keys
using the equality predicate rather than `operator==`. This is inconsistent
with the other containers but it is probably closer to user's expectations.
I have also added a `hash_value` free function so that the containers can be
hashed by [classref boost::hash].
[h2 Active Issues and Proposals]
[h3 Removing unused allocator functions]
@ -181,32 +192,14 @@ It is not specified if `unordered_multiset` and `unordered_multimap` preserve th
of elements with equivalent keys (i.e. if they're stable under `insert` and `erase`).
This is [@http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#518 issue 581].
The current proposal is that insert, erase and rehash are stable - so they are here.
(Update: during the release of this version, this requirement was added to
[@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2691.pdf
the lastest working draft]).
[h3 const_local_iterator cbegin, cend missing from TR1]
[@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2482.html#691
[@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2684.html#691
Issue 691] is that `cbegin` and `cend` are missing for local iterators.
The current resolution is that they'll be added, so I've added them.
[h2 Future Developments]
[h3 Support for `emplace`]
In __n2369__ a new member function, `emplace` was added to the containers to
allow placement insert, as described in __n2345__. To fully implement this
`std::forward` is required, along with new functions in `std::allocator` and
new constructors in `std::pair`. But partial support is possible - especially
if I don't use the `construct` member of allocators.
[h3 Equality operator]
While `operator==` and `operator!=` are not included in the standard, it's
possible to implement them for all the containers - this is helped by having
stable order of elements with equivalent keys. They will need to be specified
differently to the standard associative containers, probably comparing keys
using the equality predicate rather than `operator==`. This is inconsistent
with the other containers but it is probably closer to user's expectations.
If these are added then a `hash_value` free function should also be added.
[endsect]