[#BloombergLP-bdlcc-Cache]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/bdlcc.adoc[bdlcc]::Cache
:relfileprefix: ../../
:mrdocs:

This class represents a simple in‐process key‐value store supporting a variety of eviction policies.

== Synopsis

Declared in `<bdlcc_cache.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    class KEY,
    class VALUE,
    class HASH = xref:bsl/hash-06.adoc[bsl::hash<KEY>],
    class EQUAL = xref:bsl/equal_to-0d.adoc[bsl::equal_to<KEY>]>
class Cache;
----

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlcc/Cache/KVType.adoc[`KVType`] 
| Value type of a bulk insert entry.
| xref:BloombergLP/bdlcc/Cache/PostEvictionCallback.adoc[`PostEvictionCallback`] 
| Type of function to call after an item has been evicted from the cache.
| xref:BloombergLP/bdlcc/Cache/ValuePtrType.adoc[`ValuePtrType`] 
| Shared pointer type pointing to value type.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/bdlcc/Cache/2constructor-0a7.adoc[`Cache`]         [.small]#[constructor]#
| Constructors
| xref:BloombergLP/bdlcc/Cache/clear.adoc[`clear`] 
| Remove all items from this cache. Do _not_ invoke the post‐eviction callback.
| xref:BloombergLP/bdlcc/Cache/equalFunction.adoc[`equalFunction`] 
| Return (a copy of) the key‐equality functor used by this cache that returns `true` if two `KEY` objects have the same value, and `false` otherwise.
| xref:BloombergLP/bdlcc/Cache/erase.adoc[`erase`] 
| Remove the item having the specified `key` from this cache. Invoke the post‐eviction callback for the removed item. Return 0 on success and 1 if `key` does not exist.
| xref:BloombergLP/bdlcc/Cache/eraseBulk-0d.adoc[`eraseBulk`] 
| `eraseBulk` overloads
| xref:BloombergLP/bdlcc/Cache/evictionPolicy.adoc[`evictionPolicy`] 
| Return the eviction policy used by this cache.
| xref:BloombergLP/bdlcc/Cache/hashFunction.adoc[`hashFunction`] 
| Return (a copy of) the unary hash functor used by this cache to generate a hash value (of type `std::size_t`) for a `KEY` object.
| xref:BloombergLP/bdlcc/Cache/highWatermark.adoc[`highWatermark`] 
| Return the high watermark of this cache, which is the size at which eviction of existing items begins.
| xref:BloombergLP/bdlcc/Cache/insert-08.adoc[`insert`] 
| `insert` overloads
| xref:BloombergLP/bdlcc/Cache/insertBulk-0d.adoc[`insertBulk`] 
| `insertBulk` overloads
| xref:BloombergLP/bdlcc/Cache/lowWatermark.adoc[`lowWatermark`] 
| Return the low watermark of this cache, which is the size at which eviction of existing items ends.
| xref:BloombergLP/bdlcc/Cache/popFront.adoc[`popFront`] 
| Remove the item at the front of the eviction queue. Invoke the post‐eviction callback for the removed item. Return 0 on success, and 1 if this cache is empty.
| xref:BloombergLP/bdlcc/Cache/setPostEvictionCallback.adoc[`setPostEvictionCallback`] 
| Set the post‐eviction callback to the specified `postEvictionCallback`. The post‐eviction callback is invoked for each item evicted or removed from this cache.
| xref:BloombergLP/bdlcc/Cache/size.adoc[`size`] 
| Return the current size of this cache.
| xref:BloombergLP/bdlcc/Cache/tryGetValue.adoc[`tryGetValue`] 
| Load, into the specified `value`, the value associated with the specified `key` in this cache. If the optionally specified `modifyEvictionQueue` is `true` and the eviction policy is LRU, then move the cached item to the back of the eviction queue. Return 0 on success, and 1 if `key` does not exist in this cache. Note that a write lock is acquired only if this queue is modified.
| xref:BloombergLP/bdlcc/Cache/visit.adoc[`visit`] 
| Call the specified `visitor` for every item stored in this cache in the order of the eviction queue until `visitor` returns `false`. The `VISITOR` type must be a callable object that can be invoked in the same way as the function `bool (const KEY&, const VALUE&)`
|===


== Friends

[cols="1,4"]
|===
| Name| Description
| `xref:BloombergLP/bdlcc/Cache_TestUtil.adoc[BloombergLP::bdlcc::Cache_TestUtil]`
| This class implements a test utility that gives the test driver access to the lock / unlock method of the RW mutex. Its purpose is to allow testing that the locking actually happens as planned.
|===


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