[#bsl-unordered_map-02b-at-02]
= xref:bsl.adoc[bsl]::xref:bsl/unordered_map-02b.adoc[unordered_map]::at
:relfileprefix: ../../
:mrdocs:

Return a reference providing non‐modifiable access to the mapped‐value associated with a key that is equivalent to the specified `key`, if such an entry exists; otherwise, throw a `std::out_of_range` exception. Note that this method may also throw a different kind of exception if the (user‐supplied) comparator throws.

== Synopsis

Declared in `<bslstl_unorderedmap.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class LOOKUP_KEY>
add_lvalue_reference<VALUE const>::type
at(LOOKUP_KEY const& key) const
requires BloombergLP::bslmf::IsTransparentPredicate<HASH, LOOKUP_KEY>::value
        && BloombergLP::bslmf::IsTransparentPredicate<EQUAL,LOOKUP_KEY>::value;
----

== Description

Note: implemented inline due to Sun CC compilation error


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