[#BloombergLP-bslh-hashAppend-043]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslh.adoc[bslh]::hashAppend
:relfileprefix: ../../
:mrdocs:

Combine an optional value into the state of a hash algorithm.

== Synopsis

Declared in `<bslh_hashoptional.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class HASH_ALGORITHM,
    class TYPE>
void
hashAppend(
    HASH_ALGORITHM& algorithm,
    std::optional<TYPE> const& input);
----

== Description

If the specified `input` is engaged, pass its contained value into the specified `algorithm` to be combined into the internal state of the algorithm that is used to produce the resulting hash value. Otherwise, pass an arbitrary `size_t` value instead. Note that this behavior (for engaged values) is required by the C++ Standard.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *algorithm*
| hashing algorithm into which the value is combined
| *input*
| optional value whose contents are hashed when engaged
|===


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