Boost.Optional

lib: boost/libs/optional
repo: boostorg/optional
commit: cb7641dc, 2017-02-14

Boost Optional

Header <boost/optional.hpp> Header <boost/optional/optional_io.hpp>

Class Template `optional`

Allow bind to reference type (but not rvalue-reference)

Differences from STD proposal:

Supports bind to lvalue-reference, specialized for reference and storing pointer for them.
Constructor optional(bool, T const&) and make_optional(bool, T const&)
Constructors/assignments for optional<U>, when T can construct from U
Constructors/assignments for InPlaceFactory, and in_place_init_if_t constructors.
Member and non-member get() and get_ptr(), to get reference/pointer to stored data.
Provide value_or_eval(F)
boost::none vs. std::nullopt

Exception `bad_optional_access`

Thrown by optional::value() when it contains nothing.

I/O of `optional`

Empty optional becomes "--".
Non-empty optional having a leading space and the content value's representation.

Dependency

Boost.Config

<boost/config.hpp>, <boost/detail/workaround.hpp>

Boost.Core

<boost/core/addressof.hpp>
<boost/core/enable_if.hpp>
<boost/core/explicit_operator_bool.hpp>
<boost/core/swap.hpp>
<boost/type.hpp>

Boost.Assert

<boost/assert.hpp>

Boost.StaticAssert

<boost/static_assert.hpp>

Boost.ThrowException

<boost/throw_exception.hpp>

Boost.MPL

<boost/mpl/if.hpp>, <boost/mpl/bool.hpp>, <boost/mpl/not.hpp>

Boost.TypeTraits

<boost/type_traits/alignment_of.hpp>, <boost/type_traits/type_with_alignment.hpp>
<boost/type_traits/*.hpp> for const/reference, decay, etc.
<boost/type_traits/*.hpp> for nothrow_xxx detection
<boost/type_traits/is_same.hpp>, <boost/type_traits/is_base_of.hpp>

Boost.Move

<boost/move/utility.hpp>

Boost.Utility

<boost/utility/compare_pointees.hpp>

Standard Facilities

Standard library: <optional> (C++17)

Proposals: Library Fundamentals v1 - <optional>