Guard

(Difference between revisions)

Revision as of 18:56, 20 June 2008

XXX explain what a Guard is

to coerce(specimen, ejector :OneArgFunc) :any

The specification for this message has not been written.

to rangeSupersetOf(other :Guard) :nullOK[[[Boolean]]]

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-A Guard will either coerce an input to a value that matches some condition, or it will fail.
+XXX explain what a Guard is
-A Guard is used in the E language to guard the definition of a variable or the return value of a method. Implementors of Guard should always override __printOn/1 to print a guard expression reflecting the guard's value.
-It is planned but not yet implemented that all objects used as guards must be [[DeepFrozen]].
 ==Protocol==
-{{instance msgdoc|coerce|2|<var>specimen</var>, <var>optEjector</var> :[[nullOk]]<nowiki>[</nowiki>[[OneArgFunc]]]|[[any]]}}
+===coerce/2===
+to coerce(<var>specimen</var>, <var>ejector</var> :[[OneArgFunc]]) :[[any]]
-If <var>specimen</var> coerces to a reference that matches the condition represented by this guard, return that reference; otherwise fail (according to <var>[[optEjector]]</var>) with a [[problem]] explaining why not.
-If optEjector is [[null]], then [[throw]] the problem. Otherwise, call optEjector with the problem. optEjector should perform a non-local exit, and so should not return. If optEjector returns anyway, then throw the problem after all.
+{{unspecified message}}
-(See also: the [[non-optional ejectors]] proposal.)
+===rangeSupersetOf/1===
-{{instance msgdoc|rangeSupersetOf|1|<var>other</var> :[[Guard]]|[[nullOk]]<nowiki>[</nowiki>[[Boolean]]]}}
+to rangeSupersetOf(<var>other</var> :[[Guard]]) :[[nullOK]][[[Boolean]]]
 Experimental. See [[guard-based auditing]].