[#bsl-Pair_First-09-2constructor-0e]
= xref:bsl.adoc[bsl]::xref:bsl/Pair_First-09.adoc[Pair_First<TYPE&&>]::Pair_First
:relfileprefix: ../../
:mrdocs:

Construct the `first` member from the single element of `arg`.

== Synopsis

Declared in `<bslstl_pair.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class ARG>
constexpr
Pair_First(
    std::tuple<ARG>&& arg,
    xref:BloombergLP/bslstl/Pair_IndexSequence.adoc[BloombergLP::bslstl::Pair_IndexSequence<0U>] indices);
----

== Description

Construct the `first` member of a `pair`, forwarding in order the elements in the specified `arg` tuple to the corresponding constructor of (template parameter) `TYPE`. The length of the tuple is equal to the length of the index sequence passed to the constructor via the `Pair_IndexSequence` object.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *arg*
| single‐element tuple forwarded to the constructor of `TYPE`
| *indices*
| index sequence enumerating the elements of `arg`
|===


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