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https://issues.apache.org/jira/browse/GROOVY-10574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17524631#comment-17524631
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Eric Milles commented on GROOVY-10574:
--------------------------------------
Category is intended to reduce the boilerplate of writing category classes for
“use”, “mixin” and extension classes. The main limitation is that every method
gets the same self type.
There is lots more description in the language docs and there is probably a
mrhaki article as well.
> @NamedVariant generation does not work with extension methods
> -------------------------------------------------------------
>
> Key: GROOVY-10574
> URL: https://issues.apache.org/jira/browse/GROOVY-10574
> Project: Groovy
> Issue Type: Bug
> Affects Versions: 2.5.16, 3.0.10, 4.0.1
> Reporter: Leonard Brünings
> Priority: Major
> Labels: named-parameters
> Attachments: screenshot-1.png
>
>
> Based on the discussion in GROOVY-10567 I tried creating a extension method
> by explicitly annotating the other parameters with {{@NamedParam}}. However,
> the method was not picked up as an extension method.
> As an example:
> {code:groovy}
> import groovy.transform.*
> @NamedVariant
> static javaBlockingTest(File self,
> @NamedParam String packageName = 'com.example',
> @NamedParam String className = "BlockingTest") {
> }
> {code}
> will generate as
> {code:groovy}
> @groovy.transform.Generated
> public static java.lang.Object
> javaBlockingTest(@groovy.transform.NamedParams(value =
> [@groovy.transform.NamedParam(value = 'packageName', type =
> java.lang.String), @groovy.transform.NamedParam(value = 'className', type =
> java.lang.String)]) java.util.Map namedArgs, java.io.File self) {
> if ( namedArgs == null) {
> throw new java.lang.IllegalArgumentException('Named parameter map
> cannot be null')
> }
> for (java.lang.String namedArgKey : namedArgs.keySet()) {
> assert ['self', 'packageName', 'className'].contains( namedArgKey
> ) : 'Unrecognized namedArgKey: ' + namedArgKey }
> return this.javaBlockingTest(self,
> namedArgs.containsKey('packageName') ? namedArgs.packageName : 'com.example',
> namedArgs.containsKey('className') ? namedArgs.className : 'BlockingTest')
> }
> {code}
> Important to note is that the {{namedArgs}} parameter was moved before the
> {{self}} parameter, basically shifting the extended type from {{File}} to
> {{Map}}.
> If we handcraft
> {code:groovy}
> public static java.lang.Object javaBlockingTest(java.io.File self,
> @groovy.transform.NamedParams(value = [@groovy.transform.NamedParam(value =
> 'packageName', type = java.lang.String), @groovy.transform.NamedParam(value =
> 'className', type = java.lang.String)]) java.util.Map namedArgs) {
> }
> {code}
> it works as expected.
> IMHO we would need a flag {{@NamedVariant(extensionMethod = true)}}, which
> changes the generated code by preserving the first parameter.
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