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Documented vector's weaker exception guarantees.

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Ion Gaztañaga
2014-04-16 14:44:15 +02:00
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@@ -799,15 +799,45 @@ versions.
[endsect] [endsect]
[section:vector_exception_guarantees `vector`'s exception guarantees]
[classref ::boost::container::vector vector] does not support the strong exception guarantees
given by `std::vector` in functions like `insert`, `push_back`, `emplace`, `emplace_back`,
`resize`, `reserve` or `shrink_to_fit` for either copyable or no-throw moveable classes.
[@http://en.cppreference.com/w/cpp/utility/move_if_noexcept move_if_noexcept] is used to maintain
C++03 exception safety guarantees combined with C++11 move semantics.
This strong exception guarantee degrades the insertion performance of copyable and throw moveable types,
degrading moves to copies when such types are inserted in the vector using the aforementioned
members.
This strong exception guarantee also precludes the possibility of using some type of
in-place reallocations that can further improve the insertion performance of `vector` See
[link container.extended_functionality.extended_allocators Extended Allocators] to know more
about these optimization.
[classref ::boost::container::vector ::boost::container::vector] always uses move constructors/assignments
to rearrange elements in the vector and uses memory expansion mechanisms if the allocator supports them,
while offering only basic safety guarantees. It trades off exception guarantees for an improved performance.
[endsect]
[section:Vector_bool `vector<bool>`] [section:Vector_bool `vector<bool>`]
`vector<bool>` specialization has been quite problematic, and there have been several `vector<bool>` specialization has been quite problematic, and there have been several
unsuccessful tries to deprecate or remove it from the standard. [*Boost.Container] does not implement it unsuccessful tries to deprecate or remove it from the standard. [*Boost.Container] does not implement it
as there is a superior [@http://www.boost.org/libs/dynamic_bitset/ Boost.DynamicBitset] as there is a superior [@http://www.boost.org/libs/dynamic_bitset/ Boost.DynamicBitset]
solution. For issues with `vector<bool>` see papers solution. For issues with `vector<bool>` see the following papers:
[@http://www.gotw.ca/publications/N1211.pdf vector<bool>: N1211: More Problems, Better Solutions],
[@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2160.html N2160: Library Issue 96: Fixing vector<bool>], * [@http://home.roadrunner.com/~hinnant/onvectorbool.html On `vector<bool>`]
[@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2204.html N2204 A Specification to deprecate vector<bool>]. * [@http://www.gotw.ca/publications/N1211.pdf vector<bool>: N1211: More Problems, Better Solutions],
* [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2160.html N2160: Library Issue 96: Fixing vector<bool>],
* [@http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2204.html N2204 A Specification to deprecate vector<bool>].
Quotes:
* ["['But it is a shame that the C++ committee gave this excellent data structure the name vector<bool> and
that it gives no guidance nor encouragement on the critical generic algorithms that need to be optimized for this
data structure. Consequently, few std::lib implementations go to this trouble.]]
* ["['In 1998, admitting that the committee made a mistake was controversial. * ["['In 1998, admitting that the committee made a mistake was controversial.
Since then Java has had to deprecate such significant portions of their libraries Since then Java has had to deprecate such significant portions of their libraries
@@ -823,7 +853,7 @@ has already hurt users who have been forced to implement workarounds to disable
(e.g., by using a vector<char> and manually casting to/from bool).]] (e.g., by using a vector<char> and manually casting to/from bool).]]
So `boost::container::vector<bool>::iterator` returns real `bool` references and works as a fully compliant container. So `boost::container::vector<bool>::iterator` returns real `bool` references and works as a fully compliant container.
If you need a memory optimized version of `boost::container::vector<bool>` functionalities, please use If you need a memory optimized version of `boost::container::vector<bool>`, please use
[@http://www.boost.org/libs/dynamic_bitset/ Boost.DynamicBitset]. [@http://www.boost.org/libs/dynamic_bitset/ Boost.DynamicBitset].
[endsect] [endsect]
@@ -947,7 +977,10 @@ use [*Boost.Container]? There are several reasons for that:
[@https://svn.boost.org/trac/boost/ticket/9064 #9064], [@https://svn.boost.org/trac/boost/ticket/9064 #9064],
[@https://svn.boost.org/trac/boost/ticket/9092 #9092], [@https://svn.boost.org/trac/boost/ticket/9092 #9092],
[@https://svn.boost.org/trac/boost/ticket/9108 #9108], [@https://svn.boost.org/trac/boost/ticket/9108 #9108],
[@https://svn.boost.org/trac/boost/ticket/9166 #9166], [@https://svn.boost.org/trac/boost/ticket/9166 #9166].
* Added `default initialization` insertion functions to vector-like containers
with new overloads taking `default_init_t` as an argument instead of `const value_type &`.
[endsect] [endsect]