[#bsl-optional-072]
= xref:bsl.adoc[bsl]::optional
:relfileprefix: ../
:mrdocs:

Allocator‐aware nullable wrapper for an object of type `t_TYPE`.

== Synopsis

Declared in `<bslstl_optional.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class t_TYPE>
class optional
    : public xref:BloombergLP/bslstl/Optional_Base-05.adoc[BloombergLP::bslstl::Optional_Base<t_TYPE>]
----

== Base Classes

[cols="1,4"]
|===
| Name| Description
| `xref:BloombergLP/bslstl/Optional_Base-05.adoc[BloombergLP::bslstl::Optional_Base<t_TYPE>]`
| Component‐private class template implementing `bsl::optional`.
|===

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslstl/Optional_Base-05/allocator_type.adoc[`allocator_type`] 
| This `typedef` is an alias to `bsl::allocator<char>`.
| xref:BloombergLP/bslstl/Optional_Base-05/value_type.adoc[`value_type`] 
| Alias for the managed object type of this optional.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:bsl/optional-072/2constructor-043.adoc[`optional`]         [.small]#[constructor]#
| Constructors
| xref:bsl/optional-072/operator_assign-01.adoc[`operator=`] 
| Assignment operators
| xref:bsl/optional-072/and_then-08d.adoc[`and_then`] 
| `and_then` overloads
| xref:BloombergLP/bslstl/Optional_Base-05/emplace-02.adoc[`emplace`] 
| Destroy any contained value and construct a new one in place.
| xref:BloombergLP/bslstl/Optional_Base-05/get_allocator.adoc[`get_allocator`] 
| Return allocator used for construction of `value_type`.
| xref:BloombergLP/bslstl/Optional_Base-05/has_value.adoc[`has_value`] 
| Return `false` if this object is disengaged, and `true` otherwise.
| xref:BloombergLP/bslstl/Optional_Base-05/operator_star-0b.adoc[`operator*`] 
| Dereference operators
| xref:BloombergLP/bslstl/Optional_Base-05/operator_ptr-0a.adoc[`operator‐>`] 
| Member access operators
| xref:bsl/optional-072/or_else-09.adoc[`or_else`] 
| Return this optional if engaged; otherwise invoke `func`.
| xref:BloombergLP/bslstl/Optional_Base-05/reset.adoc[`reset`] 
| Reset this object to the default constructed state (i.e., to a disengaged state).
| xref:BloombergLP/bslstl/Optional_Base-05/swap.adoc[`swap`] 
| Exchange the values of two optionals.
| xref:bsl/optional-072/transform-09d.adoc[`transform`] 
| `transform` overloads
| xref:BloombergLP/bslstl/Optional_Base-05/value-07a.adoc[`value`] 
| `value` overloads
| xref:BloombergLP/bslstl/Optional_Base-05/value_or-07.adoc[`value_or`] 
| Return the contained value, or a converted fallback if disengaged.
| xref:BloombergLP/bslstl/Optional_Base-05/2conversion-076.adoc[`operator BloombergLP::bslmf::NestedTraitDeclaration<Optional_Base, IsBitwiseCopyable, BloombergLP::bslmf::IsBitwiseCopyable<t_TYPE>::value>`] 
| Nested trait declaration for `bslmf::IsBitwiseCopyable`.
| xref:BloombergLP/bslstl/Optional_Base-05/2conversion-04.adoc[`operator BloombergLP::bslmf::NestedTraitDeclaration<Optional_Base, IsBitwiseMoveable, BloombergLP::bslmf::IsBitwiseMoveable<t_TYPE>::value>`] 
| Nested trait declaration for `bslmf::IsBitwiseMoveable`.
| xref:BloombergLP/bslstl/Optional_Base-05/2conversion-0a.adoc[`operator BloombergLP::bslmf::NestedTraitDeclaration<Optional_Base, UsesAllocatorArgT>`] 
| Nested trait declaration for `bslmf::UsesAllocatorArgT`.
| xref:BloombergLP/bslstl/Optional_Base-05/2conversion-0b.adoc[`operator BloombergLP::bslmf::NestedTraitDeclaration<Optional_Base, UsesBslmaAllocator>`] 
| Nested trait declaration for `bslma::UsesBslmaAllocator`.
| xref:bsl/optional-072/2conversion-0af.adoc[`operator BloombergLP::bslmf::NestedTraitDeclaration<optional, IsBitwiseCopyable, BloombergLP::bslmf::IsBitwiseCopyable<t_TYPE>::value>`] 
| Nested trait declaration for `bslmf::IsBitwiseCopyable`.
| xref:bsl/optional-072/2conversion-0a1.adoc[`operator BloombergLP::bslmf::NestedTraitDeclaration<optional, IsBitwiseMoveable, BloombergLP::bslmf::IsBitwiseMoveable<t_TYPE>::value>`] 
| Nested trait declaration for `bslmf::IsBitwiseMoveable`.
| xref:bsl/optional-072/2conversion-0d.adoc[`operator BloombergLP::bslmf::NestedTraitDeclaration<optional, UsesAllocatorArgT, BloombergLP::bslma::UsesBslmaAllocator<t_TYPE>::value>`] 
| Nested trait declaration for `bslmf::UsesAllocatorArgT`.
| xref:bsl/optional-072/2conversion-05.adoc[`operator BloombergLP::bslmf::NestedTraitDeclaration<optional, UsesBslmaAllocator, BloombergLP::bslma::UsesBslmaAllocator<t_TYPE>::value>`] 
| Nested trait declaration for `bslma::UsesBslmaAllocator`.
| xref:BloombergLP/bslstl/Optional_Base-05/2conversion-071.adoc[`operator bool`] 
| Return `false` if this object is disengaged, and `true` otherwise.
|===


== Protected Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslstl/Optional_Base-05/AllocType.adoc[`AllocType`] 
| This `typedef` is an alias to `allocator_type`.
|===


== Protected Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslstl/Optional_Base-05/assignOrEmplace.adoc[`assignOrEmplace`] 
| Assign or emplace a value into this optional.
| xref:BloombergLP/bslstl/Optional_Base-05/dereferenceRaw-049.adoc[`dereferenceRaw`] 
| Return a reference to the contained value without checking engagement.
|===


== Deduction Guides

[cols="1,4"]
|===
| Name| Description
| xref:bsl/optional-0d.adoc[`optional<t_TYPE>`] 
| Deduce the specified type `t_TYPE` from the corresponding type supplied to the constructor of `optional`.
| xref:bsl/optional-0b.adoc[`optional<t_TYPE>`] 
| Deduce `t_TYPE` for an allocator‐aware optional from a value.
| xref:bsl/optional-07d.adoc[`optional<t_TYPE>`] 
| Deduce `t_TYPE` for an allocator‐aware optional from another optional.
|===


== Friends

[cols="1,4"]
|===
| Name| Description
| `bsl::optional`
| Allocator‐aware nullable wrapper for an object of type `t_TYPE`.
|===

== Non-Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:bsl/PrintTo-0f.adoc[`PrintTo`]
| Write the specified `value` to the specified `*stream`, surrounded by double quotes.
| xref:bsl/make_optional-00.adoc[`make_optional`]
| Return an `optional` containing a value constructed from the arguments.
| xref:bsl/make_optional-01.adoc[`make_optional`]
| Return an `optional` object containing a value‐initialized `t_TYPE` object.
| xref:bsl/make_optional-03.adoc[`make_optional`]
| Return an `optional` containing a value constructed from the arguments.
| xref:bsl/make_optional-04.adoc[`make_optional`]
| Return an `optional` containing a value constructed from the arguments.
| xref:bsl/make_optional-06.adoc[`make_optional`]
| Return an `optional` containing a value constructed from the arguments.
| xref:bsl/make_optional-0a.adoc[`make_optional`]
| Return an `optional` containing a value constructed from the arguments.
| xref:bsl/make_optional-0e.adoc[`make_optional`]
| Return an `optional` containing a value constructed from the arguments.
| xref:bsl/operator_not_eq-0c3.adoc[`operator!=`]
| Return whether the operands do not have the same value.
| xref:bsl/operator_not_eq-0cf.adoc[`operator!=`]
| Return whether the operands do not have the same value.
| xref:bsl/operator_not_eq-0e.adoc[`operator!=`]
| Return whether the operands do not have the same value.
| xref:bsl/operator_lt-00.adoc[`operator<`]
| Return whether the left‐hand operand is ordered before the right.
| xref:bsl/operator_lt-010.adoc[`operator<`]
| Return whether the left‐hand operand is ordered before the right.
| xref:bsl/operator_lt-0b.adoc[`operator<`]
| Return whether the left‐hand operand is ordered before the right.
| xref:bsl/operator_le-03.adoc[`operator<=`]
| Return whether the left‐hand operand is before or equal to the right.
| xref:bsl/operator_le-04.adoc[`operator<=`]
| Return whether the left‐hand operand is before or equal to the right.
| xref:bsl/operator_le-0c.adoc[`operator<=`]
| Return whether the left‐hand operand is before or equal to the right.
| xref:bsl/operator_3way-00.adoc[`operator<=>`]
| Perform a three‐way comparison of the operands.
| xref:bsl/operator_3way-070.adoc[`operator<=>`]
| Perform a three‐way comparison of the operands.
| xref:bsl/operator_3way-0a.adoc[`operator<=>`]
| Perform a three‐way comparison of the operands.
| xref:bsl/operator_3way-0d1.adoc[`operator<=>`]
| Perform a three‐way comparison of the operands.
| xref:bsl/operator_eq-02a.adoc[`operator==`]
| Return whether the operands have the same value.
| xref:bsl/operator_eq-097.adoc[`operator==`]
| Return whether the operands have the same value.
| xref:bsl/operator_eq-09de.adoc[`operator==`]
| Compare a `std::optional` with a `bsl::optional` for equality.
| xref:bsl/operator_eq-0db.adoc[`operator==`]
| Return whether the operands have the same value.
| xref:bsl/operator_gt-04.adoc[`operator>`]
| Return whether the left‐hand operand is ordered after the right.
| xref:bsl/operator_gt-07.adoc[`operator>`]
| Return whether the left‐hand operand is ordered after the right.
| xref:bsl/operator_gt-0bc.adoc[`operator>`]
| Return whether the left‐hand operand is ordered after the right.
| xref:bsl/operator_ge-05.adoc[`operator>=`]
| Return whether the left‐hand operand is after or equal to the right.
| xref:bsl/operator_ge-06.adoc[`operator>=`]
| Return whether the left‐hand operand is after or equal to the right.
| xref:bsl/operator_ge-088.adoc[`operator>=`]
| Return whether the left‐hand operand is after or equal to the right.
| xref:bsl/swap-00c.adoc[`swap`]
| Exchange the values of two optionals.
| xref:bsl/swap-04d.adoc[`swap`]
| Exchange the values of two optionals.
| xref:bsl/swap-0f3.adoc[`swap`]
| Exchange the values of two optionals.
| xref:BloombergLP/bdlb/nullableValue_acceptsBslOptional.adoc[`::BloombergLP::bdlb::nullableValue_acceptsBslOptional`]
| Component‐private constraint helper for `bsl::optional` conversion.
| xref:BloombergLP/bdlb/operator_not_eq-07b.adoc[`::BloombergLP::bdlb::operator!=`]
| Return `true` if the specified nullable objects do not have the same value.
| xref:BloombergLP/bdlb/operator_not_eq-0a1.adoc[`::BloombergLP::bdlb::operator!=`]
| Return `true` if the specified nullable objects do not have the same value.
| xref:BloombergLP/bdlb/operator_lt-07.adoc[`::BloombergLP::bdlb::operator<`]
| Return `true` if `lhs` is ordered before `rhs`, and `false` otherwise.
| xref:BloombergLP/bdlb/operator_lt-0b.adoc[`::BloombergLP::bdlb::operator<`]
| Return whether the left‐hand operand is ordered before the right.
| xref:BloombergLP/bdlb/operator_le-041.adoc[`::BloombergLP::bdlb::operator<=`]
| Return whether the left‐hand operand is before or equal to the right.
| xref:BloombergLP/bdlb/operator_le-06b.adoc[`::BloombergLP::bdlb::operator<=`]
| Return `true` if `lhs` is ordered before `rhs` or they are equal.
| xref:BloombergLP/bdlb/operator_eq-047.adoc[`::BloombergLP::bdlb::operator==`]
| Return `true` if the specified nullable objects have the same value.
| xref:BloombergLP/bdlb/operator_eq-052.adoc[`::BloombergLP::bdlb::operator==`]
| Return `true` if the specified nullable objects have the same value, and `false` otherwise.
| xref:BloombergLP/bdlb/operator_gt-00.adoc[`::BloombergLP::bdlb::operator>`]
| Return `true` if `lhs` is ordered after `rhs`, and `false` otherwise.
| xref:BloombergLP/bdlb/operator_gt-04b.adoc[`::BloombergLP::bdlb::operator>`]
| Return whether the left‐hand operand is ordered after the right.
| xref:BloombergLP/bdlb/operator_ge-01d1.adoc[`::BloombergLP::bdlb::operator>=`]
| Return whether the left‐hand operand is after or equal to the right.
| xref:BloombergLP/bdlb/operator_ge-087.adoc[`::BloombergLP::bdlb::operator>=`]
| Return `true` if `lhs` is ordered after `rhs` or they are equal.
| xref:BloombergLP/bslstl/optional_acceptsBslOptional.adoc[`::BloombergLP::bslstl::optional_acceptsBslOptional`]
| Component‐private constraint helper for `Optional_DerivedFromBslOptional`.
|===

== Derived Classes

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlb/NullableValue.adoc[`NullableValue`] 
| Value‐semantic wrapper that adds a null state to `TYPE`.
|===


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