[/
    Boost.Optional

    Copyright (c) 2015 Andrzej Krzemienski

    Distributed under the Boost Software License, Version 1.0.
    (See accompanying file LICENSE_1_0.txt or copy at
    http://www.boost.org/LICENSE_1_0.txt)
]


[section:relnotes Release Notes]

[heading Boost Release X.XX]

* Changed the implementation of `boost::none`: now it is a constant with internal linkage. This addresses [@https://svn.boost.org/trac/boost/ticket/11203 Trac #11203].
* Now `boost::optional` is specialized for reference parameters. This way the `sizeof` of optional reference is that of a pointer, and a number of bugs is avoided.

[heading Boost Release 1.59]

* For C++03 compilers, added 0-argument overload for member function `emplace()`, and therewith removed the dependency on `<boost/utility/in_place_factory.hpp>`.

[heading Boost Release 1.58]

* `boost::none_t` is no longer convertible from literal `0`. This avoids a bug where `optional<rational<int>> oi = 0;` would initialize an optional object with no contained value.
* Improved the trick that prevents streaming out `optional` without header `optional_io.hpp` by using safe-bool idiom. This addresses [@https://svn.boost.org/trac/boost/ticket/10825 Trac #10825].
* IOStream operators are now mentioned in documentation.
* Added a way to manually disable move semantics: just define macro `BOOST_OPTIONAL_CONFIG_NO_RVALUE_REFERENCES`. This can be used to work around [@https://svn.boost.org/trac/boost/ticket/10399 Trac #10399].
* It is no longer possible to assign `optional<U>` to `optional<T>` when `U` is not assignable or convertible to `T` ([@https://svn.boost.org/trac/boost/ticket/11087 Trac #11087]).
* Value accessors now work correctly on rvalues of `optional<T&>` ([@https://svn.boost.org/trac/boost/ticket/10839 Trac #10839]).  


[heading Boost Release 1.57]

* [@https://github.com/boostorg/optional/pull/9 Git pull #9]: ['"Supply `<string>` to fix C++03 compile error on `logic_error("...")`"].


[heading Boost Release 1.56]

* Added support for rvalue references. Now `optional<T>` works with moveable but non-copyable `T`'s,
* Improved `swap` (now uses move operations),
* Added function `emplace()`. This is the last of the requests from [@https://svn.boost.org/trac/boost/ticket/1841 Trac #1841],
* `optional` is moveable, including conditional `noexcept` specifications, which make it `move_if_noexcept`-friendly,
* Using explicit operator bool() on platforms that support it ([@https://svn.boost.org/trac/boost/ticket/4227 Trac #4227]) (breaking change),
* Forward declaration of `operator<<(ostream&, optional const&)` to prevent inadvertent incorrect serialization of optional objects,
* Removed deprecated function `reset()` from examples ([@https://svn.boost.org/trac/boost/ticket/9005 Trac #9005]),
* Equality comparison with `boost::none` does not require that `T` be EqualityComparable,
* Optional rvalue references are explicitly disallowed,
* Binding temporaries to optional references is explicitly disallowed (breaking change),
* More ways to access the contained value, functions `value()`, `value_or()`, `value_or_eval()`,
* Updated and reorganized documentation, added tutorial and quick guide sections.



[endsect][/ relnotes]