[#llvm-find_singleton_nested]
= xref:llvm.adoc[llvm]::find_singleton_nested
:relfileprefix: ../
:mrdocs:

Return the nested singleton match in `Range,` or a failure pair.

== Synopsis

Declared in `<llvm/ADT/STLExtras.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    typename T,
    typename R,
    typename Predicate>
std::pair<T*, bool>
find_singleton_nested(
    R&& Range,
    Predicate P,
    bool AllowRepeats = false);
----

== Description

`P` returns std::pair<T *, bool> where the pointer is the candidate and the bool reports that multiples were already found. Returns nullptr when no values or multiple values were found, with a bool indicating whether multiples caused the nullptr. When `AllowRepeats` is true, multiple equal values are allowed. It is expected that first is nullptr when second is true. This allows using find_singleton_nested within the predicate `P.`

== Return Value

Pair of the singleton match and whether multiples caused failure.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *Range*
| Range to search.
| *P*
| Nested singleton predicate.
| *AllowRepeats*
| Whether equal repeats of the same value are allowed.
|===


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