[#bsl-Pair_First-00-2constructor-0a7]
= xref:bsl.adoc[bsl]::xref:bsl/Pair_First-00.adoc[Pair_First]::Pair_First
:relfileprefix: ../../
:mrdocs:

Constructors

== Synopses

Declared in `<bslstl_pair.h>`

Value‐initialize the 'first' member of a 'pair'. This constructor is declared only if (template parameter) `TYPE` is default constructible.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
constexpr
xref:bsl/Pair_First-00/2constructor-0c9.adoc[Pair_First]()
requires std::is_default_constructible_v<TYPE>;
----

[.small]#xref:bsl/Pair_First-00/2constructor-0c9.adoc[_» more..._]#

Construct the `first` member from the specified non‐modifiable `value`, without specifying an allocator.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
constexpr
explicit
xref:bsl/Pair_First-00/2constructor-0d7.adoc[Pair_First](bsl::add_lvalue_reference<TYPE const>::type value);
----

[.small]#xref:bsl/Pair_First-00/2constructor-0d7.adoc[_» more..._]#

Construct the `first` member from the specified `value`.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class PARAM,
    class = void>
requires !bsl::is_same<Pair_First, bsl::remove_cvref_t<PARAM>>::value
constexpr
explicit
xref:bsl/Pair_First-00/2constructor-04.adoc[Pair_First](PARAM&& value);
----

[.small]#xref:bsl/Pair_First-00/2constructor-04.adoc[_» more..._]#

Construct the `first` member using the `allocator_arg` idiom.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
xref:bsl/Pair_First-00/2constructor-0ae.adoc[Pair_First](
    xref:BloombergLP/bslma/Allocator.adoc[BloombergLP::bslma::Allocator]* basicAllocator,
    xref:bsl/Pair_BslmaIdiomAllocatorArgT.adoc[Pair_BslmaIdiomAllocatorArgT] idiom);
----

[.small]#xref:bsl/Pair_First-00/2constructor-0ae.adoc[_» more..._]#

Construct the `first` member with the allocator as the last argument.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
xref:bsl/Pair_First-00/2constructor-0e.adoc[Pair_First](
    xref:BloombergLP/bslma/Allocator.adoc[BloombergLP::bslma::Allocator]* basicAllocator,
    xref:bsl/Pair_BslmaIdiomAtEnd.adoc[Pair_BslmaIdiomAtEnd] idiom);
----

[.small]#xref:bsl/Pair_First-00/2constructor-0e.adoc[_» more..._]#

Construct the `first` member of a `pair` with no allocator argument.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
xref:bsl/Pair_First-00/2constructor-05.adoc[Pair_First](
    xref:BloombergLP/bslma/Allocator.adoc[BloombergLP::bslma::Allocator]* basicAllocator,
    xref:bsl/Pair_BslmaIdiomNone.adoc[Pair_BslmaIdiomNone] idiom);
----

[.small]#xref:bsl/Pair_First-00/2constructor-05.adoc[_» more..._]#

Construct the `first` member from the elements of `argsPack`.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class... ARGS,
    size_t I...>
xref:bsl/Pair_First-00/2constructor-02.adoc[Pair_First](
    std::tuple<ARGS...>&& argsPack,
    xref:BloombergLP/bslstl/Pair_IndexSequence.adoc[BloombergLP::bslstl::Pair_IndexSequence<I...>] indices);
----

[.small]#xref:bsl/Pair_First-00/2constructor-02.adoc[_» more..._]#

Construct the `first` member using the specified `value` and `basicAllocator`, with `Pair_BslmaIdiomAllocatorArgT` placement.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class PARAM>
xref:bsl/Pair_First-00/2constructor-0dc.adoc[Pair_First](
    PARAM&& value,
    xref:BloombergLP/bslma/Allocator.adoc[BloombergLP::bslma::Allocator]* basicAllocator,
    xref:bsl/Pair_BslmaIdiomAllocatorArgT.adoc[Pair_BslmaIdiomAllocatorArgT] idiom);
----

[.small]#xref:bsl/Pair_First-00/2constructor-0dc.adoc[_» more..._]#

Construct the `first` member using the specified `value` and `basicAllocator`, with `Pair_BslmaIdiomAtEnd` placement.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class PARAM>
xref:bsl/Pair_First-00/2constructor-0a5.adoc[Pair_First](
    PARAM&& value,
    xref:BloombergLP/bslma/Allocator.adoc[BloombergLP::bslma::Allocator]* basicAllocator,
    xref:bsl/Pair_BslmaIdiomAtEnd.adoc[Pair_BslmaIdiomAtEnd] idiom);
----

[.small]#xref:bsl/Pair_First-00/2constructor-0a5.adoc[_» more..._]#

Construct the `first` member from `value`, ignoring the allocator.


[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class PARAM>
xref:bsl/Pair_First-00/2constructor-0c0.adoc[Pair_First](
    PARAM&& value,
    xref:BloombergLP/bslma/Allocator.adoc[BloombergLP::bslma::Allocator]* basicAllocator,
    xref:bsl/Pair_BslmaIdiomNone.adoc[Pair_BslmaIdiomNone] idiom);
----

[.small]#xref:bsl/Pair_First-00/2constructor-0c0.adoc[_» more..._]#

== Parameters

[cols="1,4"]
|===
| Name| Description
| *value*
| value copied into the `first` member
| *basicAllocator*
| allocator used to supply memory
| *idiom*
| tag selecting the `allocator_arg` construction idiom
| *argsPack*
| tuple of arguments forwarded to the constructor of `TYPE`
| *indices*
| index sequence enumerating the elements of `argsPack`
|===


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