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Subject: Re: static propertyMissing in an interface
From: OC <ocs@ocs.cz>
In-Reply-To: <5700A8CD.50108@gmx.org>
Date: Sun, 3 Apr 2016 17:33:54 +0200
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To: users@groovy.apache.org

Jochen,

On 3. 4. 2016, at 7:23, Jochen Theodorou <blackdrag@gmx.org> wrote:

> On 01.04.2016 03:48, OC wrote:
>> playing with possibilities of the i/i pattern, I have found one can =
install a static property to an interface, and then use the property all =
right -- see a proof-of-concept below.
>>=20
>> Since it might be used e.g. to create instances or to get a factory =
through public API based on interfaces (which would otherwise not be =
possible without exposing the implementation class), this is truly =
interesting.
>>=20
>> The question is: can I rely on this rather arcane behaviour, that it =
will not be broken in future Groovy versions?
>=20
> if you want to be really sure it will continue working it is best if =
you contribute a test case ;) But I see no plans to change that, =
especially with java8 being able to define static methods and thus =
static properties.

Thanks a lot!

> [...]
>>       def body=3D{-> "<$name in $delegate>" }
>>       delegate.metaClass.static."$getter"=3Dbody
>>       delegate."$getter"() // I wonder why just "body()" does not =
work?!?
>=20
> no idea why not... but you can always try body.call() instead.

Same as with body():

=3D=3D=3D
6 /tmp> <q.groovy=20
class q {
 static main(av) {
   ExpandoMetaClass.enableGlobally()
   Root.metaClass.static.propertyMissing=3D{ name ->
     String getter=3D"get${name.capitalize()}"
     def body=3D{-> "<$name in $delegate>" }
     delegate.metaClass.static."$getter"=3Dbody
     body.call() // same problem with body(); delegate."$getter"() would =
work though
   }
   println "- ${Root.weird}"
 }
}
interface Root {}
7 /tmp> groovy q.groovy
Caught: groovy.lang.MissingMethodException: No signature of method: =
java.io.StringWriter.capitalize() is applicable for argument types: () =
values: []
groovy.lang.MissingMethodException: No signature of method: =
java.io.StringWriter.capitalize() is applicable for argument types: () =
values: []
	at q$_main_closure1.doCall(q.groovy:5)
	at q.main(q.groovy:10)
8 /tmp>=20
=3D=3D=3D

Thanks again and all the best,
OC