Guard
From Erights
m (fixing it a bit better (replaced the underscore with an space)) |
(reverted edit -- "DeepFrozen" is preferable to "Deep Frozen" since the former matches the name used in the language) |
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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. | 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 [[ | + | It is planned but not yet implemented that all objects used as guards must be [[DeepFrozen]]. |
==Protocol== | ==Protocol== | ||
Latest revision as of 07:56, 18 September 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.
