[#beman-optional-optional-06-2constructor-03]
= xref:beman.adoc[beman]::xref:beman/optional.adoc[optional]::xref:beman/optional/optional-06.adoc[optional<T&>]::optional
:relfileprefix: ../../../
:mrdocs:

Constructors

== Synopses

Declared in `<beman/optional/optional.hpp>`

Default constructor.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
constexpr
xref:beman/optional/optional-06/2constructor-070.adoc[optional]() noexcept = default;
----

[.small]#xref:beman/optional/optional-06/2constructor-070.adoc[_» more..._]#

Copy constructor.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
constexpr
xref:beman/optional/optional-06/2constructor-0a3d.adoc[optional](xref:beman/optional/optional-06.adoc[optional] const& rhs) noexcept = default;
----

[.small]#xref:beman/optional/optional-06/2constructor-0a3d.adoc[_» more..._]#

Constructs an empty optional.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
constexpr
xref:beman/optional/optional-06/2constructor-008.adoc[optional](xref:beman/optional/nullopt_t.adoc[nullopt_t] value) noexcept;
----

[.small]#xref:beman/optional/optional-06/2constructor-008.adoc[_» more..._]#

Constructs an optional from another optional of type U


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class U>
requires (std::is_constructible_v<T&, U&> && !std::is_same_v<std::remove_cv_t<T>, optional<U>> &&
                 !std::is_same_v<T&, U> && detail::reference_constructs_from_temporary_v<T&, U&>)
constexpr
xref:beman/optional/optional-06/2constructor-01d.adoc[optional](xref:beman/optional/optional-03.adoc[optional<U>]& rhs) = delete;
----

[.small]#xref:beman/optional/optional-06/2constructor-01d.adoc[_» more..._]#

Constructs an optional from another optional of type U.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class U>
requires (std::is_constructible_v<T&, U&> && !std::is_same_v<std::remove_cv_t<T>, optional<U>> &&
             !std::is_same_v<T&, U> && !detail::reference_constructs_from_temporary_v<T&, U&>)
constexpr
explicit(!std::is_convertible_v<U &, T &>)
xref:beman/optional/optional-06/2constructor-0fa.adoc[optional](xref:beman/optional/optional-03.adoc[optional<U>]& rhs) noexcept(std::is_nothrow_constructible_v<T &, U &>);
----

[.small]#xref:beman/optional/optional-06/2constructor-0fa.adoc[_» more..._]#

Constructs an optional from another optional of type U


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class U>
requires (std::is_constructible_v<T&, const U&> && !std::is_same_v<std::remove_cv_t<T>, optional<U>> &&
                 !std::is_same_v<T&, U> && detail::reference_constructs_from_temporary_v<T&, const U&>)
constexpr
xref:beman/optional/optional-06/2constructor-07d.adoc[optional](xref:beman/optional/optional-03.adoc[optional<U>] const& rhs) = delete;
----

[.small]#xref:beman/optional/optional-06/2constructor-07d.adoc[_» more..._]#

Constructs an optional from another optional of type U.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class U>
requires (std::is_constructible_v<T&, const U&> && !std::is_same_v<std::remove_cv_t<T>, optional<U>> &&
             !std::is_same_v<T&, U> && !detail::reference_constructs_from_temporary_v<T&, const U&>)
constexpr
explicit(!std::is_convertible_v<const U &, T &>)
xref:beman/optional/optional-06/2constructor-0a31.adoc[optional](xref:beman/optional/optional-03.adoc[optional<U>] const& rhs) noexcept(std::is_nothrow_constructible_v<T &, const U &>);
----

[.small]#xref:beman/optional/optional-06/2constructor-0a31.adoc[_» more..._]#

Construct from a U


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class U>
requires (std::is_constructible_v<T&, U> && !(std::is_same_v<std::remove_cvref_t<U>, in_place_t>) &&
                 !(std::is_same_v<std::remove_cvref_t<U>, optional>) &&
                 !detail::reference_constructs_from_temporary_v<T&, U>)
constexpr
explicit(!std::is_convertible_v<U, T &>)
xref:beman/optional/optional-06/2constructor-01a.adoc[optional](U&& u) noexcept(std::is_nothrow_constructible_v<T &, U>);
----

[.small]#xref:beman/optional/optional-06/2constructor-01a.adoc[_» more..._]#

Constructs an optional from a U, but deletes the constructor if


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class U>
requires (std::is_constructible_v<T&, U> && !(std::is_same_v<std::remove_cvref_t<U>, in_place_t>) &&
                 !(std::is_same_v<std::remove_cvref_t<U>, optional>) &&
                 detail::reference_constructs_from_temporary_v<T&, U>)
constexpr
xref:beman/optional/optional-06/2constructor-004.adoc[optional](U&& u) = delete;
----

[.small]#xref:beman/optional/optional-06/2constructor-004.adoc[_» more..._]#

Constructs an optional from another optional of type U


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class U>
requires (std::is_constructible_v<T&, U> && !std::is_same_v<std::remove_cv_t<T>, optional<U>> &&
                 !std::is_same_v<T&, U> && detail::reference_constructs_from_temporary_v<T&, U>)
constexpr
xref:beman/optional/optional-06/2constructor-0a36.adoc[optional](xref:beman/optional/optional-03.adoc[optional<U>]&& rhs) = delete;
----

[.small]#xref:beman/optional/optional-06/2constructor-0a36.adoc[_» more..._]#

Constructs an optional from another optional of type U.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class U>
requires (std::is_constructible_v<T&, U> && !std::is_same_v<std::remove_cv_t<T>, optional<U>> &&
             !std::is_same_v<T&, U> && !detail::reference_constructs_from_temporary_v<T&, U>)
constexpr
explicit(!std::is_convertible_v<U, T &>)
xref:beman/optional/optional-06/2constructor-08.adoc[optional](xref:beman/optional/optional-03.adoc[optional<U>]&& rhs) noexcept(noexcept(std::is_nothrow_constructible_v<T &, U>));
----

[.small]#xref:beman/optional/optional-06/2constructor-08.adoc[_» more..._]#

Constructs an optional from another optional of type U


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class U>
requires (std::is_constructible_v<T&, const U> && !std::is_same_v<std::remove_cv_t<T>, optional<U>> &&
                 !std::is_same_v<T&, U> && detail::reference_constructs_from_temporary_v<T&, const U>)
constexpr
xref:beman/optional/optional-06/2constructor-04.adoc[optional](xref:beman/optional/optional-03.adoc[optional<U>] const&& rhs) = delete;
----

[.small]#xref:beman/optional/optional-06/2constructor-04.adoc[_» more..._]#

Constructs an optional from another optional of type U.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class U>
requires (std::is_constructible_v<T&, const U> && !std::is_same_v<std::remove_cv_t<T>, optional<U>> &&
             !std::is_same_v<T&, U> && !detail::reference_constructs_from_temporary_v<T&, const U>)
constexpr
explicit(!std::is_convertible_v<const U, T &>)
xref:beman/optional/optional-06/2constructor-05.adoc[optional](xref:beman/optional/optional-03.adoc[optional<U>] const&& rhs) noexcept(noexcept(std::is_nothrow_constructible_v<T &, const U>));
----

[.small]#xref:beman/optional/optional-06/2constructor-05.adoc[_» more..._]#

In‐place constructor.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class Arg>
requires (std::is_constructible_v<T&, Arg> && !detail::reference_constructs_from_temporary_v<T&, Arg>)
constexpr
explicit
xref:beman/optional/optional-06/2constructor-0f8.adoc[optional](
    xref:beman/optional/in_place_t.adoc[in_place_t],
    Arg&& arg);
----

[.small]#xref:beman/optional/optional-06/2constructor-0f8.adoc[_» more..._]#


[.small]#Created with https://www.mrdocs.com[MrDocs]#