Guard
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Kevin Reid (Talk | contribs) (copy in documentation from Guard.java in E-on-Java with permission) |
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==Protocol== | ==Protocol== | ||
| - | + | {{instance msgdoc|coerce|2|<var>specimen</var>, <var>optEjector</var> :[[nullOk]]<nowiki>[</nowiki>[[OneArgFunc]]]|[[any]]}} | |
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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 <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. | ||
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(See also: the [[non-optional ejectors]] proposal.) | (See also: the [[non-optional ejectors]] proposal.) | ||
| - | + | {{instance msgdoc|rangeSupersetOf|1|<var>other</var> :[[Guard]]|[[nullOk]]<nowiki>[</nowiki>[[Boolean]]]}} | |
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Experimental. See [[guard-based auditing]]. | Experimental. See [[guard-based auditing]]. | ||
Revision as of 02:22, 2 July 2008
A Guard will either coerce an input to a value that matches some condition, or it will fail.
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
coerce/2
- Signature: coerce(specimen, optEjector :nullOk[OneArgFunc]) :any
If specimen coerces to a reference that matches the condition represented by this guard, return that reference; otherwise fail (according to optEjector) 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.
(See also: the non-optional ejectors proposal.)
rangeSupersetOf/1
Experimental. See guard-based auditing.
