[#BloombergLP-ball-AttributeContext_RuleEvaluationCache]
= xref:BloombergLP.adoc[BloombergLP]::xref:BloombergLP/ball.adoc[ball]::AttributeContext_RuleEvaluationCache
:relfileprefix: ../../
:mrdocs:

This is an implementation type of `AttributeContext` and should not be used by clients of this package. A rule evaluation cache is a mechanism for evaluating and caching whether a rule is active. A rule is considered active if all of its attributes are satisfied by the collection of attributes held in a `AttributeContainerList` object (i.e., `Rule::evaluate` returns `true` for the `AttributeContainerList` object). The rules this cache evaluates are contained in a `RuleSet` object. `RuleSet::MaskType` is a bit mask for a rule set, where each bit is a boolean value associated with the rule at the corresponding index in a rule set. An `AttributeContext` determines, using the `isDataAvailable` method, if a particular set of rules (described using a bit mask) have already been evaluated. A context accesses the current cache of rule evaluations using the `knownActiveRules` method. Finally, a context updates the cache of rule evaluations using the `update` method. Note that the `isDataAvailable` method should be used prior to using `knownActiveRules` in order to ensure the relevant rules have been evaluated and that those evaluations are up‐to‐date.

== Synopsis

Declared in `<ball_attributecontext.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
class AttributeContext_RuleEvaluationCache;
----

== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:BloombergLP/ball/AttributeContext_RuleEvaluationCache/2constructor.adoc[`AttributeContext_RuleEvaluationCache`]         [.small]#[constructor]#
| Create an empty rule evaluation cache having a sequence number of ‐1.
| xref:BloombergLP/ball/AttributeContext_RuleEvaluationCache/clear.adoc[`clear`] 
| Clear any currently cached rule evaluation data, restoring this object to its default constructed state (empty).
| xref:BloombergLP/ball/AttributeContext_RuleEvaluationCache/isDataAvailable.adoc[`isDataAvailable`] 
| Return `true` if this cache contains up‐to‐date cached rule evaluations having the specified `sequenceNumber` for the set of rules indicated by the specified `relevantRulesMask` bit mask, and `false` otherwise.
| xref:BloombergLP/ball/AttributeContext_RuleEvaluationCache/knownActiveRules.adoc[`knownActiveRules`] 
| Return a bit mask indicating those rules, from the set of rules provided in the last call to `update`, that are known to be active (as of that last call to `update`). If a bit in the returned value is set to 1, the rule at the corresponding index is active; however, if a bit is set to 0, the corresponding rule is either not active _or_ has not been evaluated. Note that `isDataAvailable` should be called to test if this cache contains up‐to‐date evaluated rule information for the rules in which they are interested before using the result of this method.
| xref:BloombergLP/ball/AttributeContext_RuleEvaluationCache/print.adoc[`print`] 
| Format this object to the specified output `stream` at the (absolute value of) the optionally specified indentation `level` and return a reference to `stream`. If `level` is specified, optionally specify `spacesPerLevel`, the number of spaces per indentation level for this and all of its nested objects. If `level` is negative, suppress indentation of the first line. If `spacesPerLevel` is negative, format the entire output on one line, suppressing all but the initial indentation (as governed by `level`). If `stream` is not valid on entry, this operation has no effect.
| xref:BloombergLP/ball/AttributeContext_RuleEvaluationCache/update.adoc[`update`] 
| Update, for the specified `sequenceNumber`, the cache for those rules indicated by the specified `relevantRulesMask` bit mask in the specified set of `rules`, by evaluating those rules for the specified `attributes`; return the bit mask indicating those rules that are known to be active. If a bit in the returned bit mask value is set to 1, the rule at the corresponding index in `rules` is "active"; however, if a bit is set to 0, the corresponding rule is either not active _or_ has not been evaluated. This operation does, however, guarantee that all the rules indicated by the `relevantRulesMask` _will_ be evaluated. A particular rule is considered "active" if all of its attributes are satisfied by `attributes` (i.e., if `Rule::evaluate` returns `true` for `attributes`). The behavior is undefined unless `rules` is not modified during this operation (i.e., any lock associated with `rules` must be locked during this operation).
|===



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