[#BloombergLP-bslh-Hash-07]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bslh.adoc[bslh]::Hash
:relfileprefix: ../../
:mrdocs:

This struct wraps the (template parameter) type `HASH_ALGORITHM` in an interface that satisfies the `hash` requirements of the C++11 standard.

== Synopsis

Declared in `<bslh_hash.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<class HASH_ALGORITHM = xref:BloombergLP/bslh/DefaultHashAlgorithm.adoc[bslh::DefaultHashAlgorithm]>
struct Hash;
----

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslh/Hash-07/HashAlgorithm.adoc[`HashAlgorithm`] 
| Make the `HASH_ALGORITHM` template parameter available to clients.
| xref:BloombergLP/bslh/Hash-07/result_type.adoc[`result_type`] 
| The type of the hash value that will be returned by the function‐call operator.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslh/Hash-07/operator_call.adoc[`operator()`] 
| Returns a hash value generated by the (template parameter) type `HASH_ALGORITHM` for the specified `type`. The value returned by the `HASH_ALGORITHM` is cast to `size_t` before returning.
|===


== Specializations

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bslh/Hash-02.adoc[`Hash<>`] 
| This struct wraps the (template parameter) type `HASH_ALGORITHM` in an interface that satisfies the `hash` requirements of the C++11 standard.
| xref:BloombergLP/bslh/Hash-0a.adoc[`Hash<std::filesystem::path>`] 
| Specialization of `hash` for `std::filesystem::path` values.
|===


== Derived Classes

[cols="1,4"]
|===
| Name| Description
| xref:bsl/hash-017.adoc[`hash<basic_string<CHAR_TYPE, CHAR_TRAITS, ALLOCATOR>>`] 
| Specialize `bsl::hash` for strings, including an overload for pointers to allow character arrays to be hashed without converting them first.
| xref:bsl/hash-06.adoc[`hash`] 
| Empty base class for hashing. This class, and all explicit and partial specializations of this class, shall conform to the C++11 Hash Requirements (C++11 17.6.3.4, [hash.requirements]). Unless this template is explicitly specialized, it will use the default hash algorithm provided by `bslh::Hash<>` to supply hash values. In order to hash a user‐defined type using `bsl::hash`, `bsl::hash` must be explicitly specialized for the type, or, preferably, `hashAppend` must be implemented for the type. For more details on `hashAppend` and `bslh::Hash` see the component `bslh_hash`.
|===


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