[#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 of a `pair`, using the specified `basicAllocator` to supply memory. This constructor is selected when (template parameter) `TYPE` takes a `bslma`‐style allocator as the second constructor argument preceded by `bsl::allocator_arg`.


[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]);
----

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

Construct the `first` member of a `pair`, using the specified `basicAllocator` to supply memory. This constructor is selected when (template parameter) `TYPE` takes a `bslma`‐style allocator as the last constructor 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]);
----

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

Construct the `first` member of a `pair`, using the specified `basicAllocator` to supply memory. Note that exactly one of these three constructors is enabled at compile‐time for (template parameter) type `TYPE` based on the following respective criteria: 1) `TYPE` does not support `bslma`‐style allocators, 2) `TYPE` takes a `bslma`‐style allocator as the last constructor argument, and 3) `TYPE` takes a `bslma`‐style allocator as the second constructor argument preceded by `bsl::allocator_arg`.


[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]);
----

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

Construct the `first` member of a `pair`, forwarding in order the elements in the specified `argsPack` to the corresponding constructor of (template parameter) `TYPE`. The length of the `argsPack` is equal to the length of the specified (template parameter pack) `I...` and passed to the constructor via the `Pair_IndexSequence` object.


[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...>]);
----

[.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]);
----

[.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]);
----

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

Construct the 'first' member of a 'pair' from the specified 'value', using the specified 'basicAllocator' to supply memory. This function (perfectly) forwards 'value' to the constructor of (template parameter) 'TYPE' when 'TYPE' does not use 'bslma'‐style allocators.


[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]);
----

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


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