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https://issues.apache.org/jira/browse/GROOVY-11143?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17750028#comment-17750028
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Jochen Theodorou commented on GROOVY-11143:
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It depends on if you want to limit the visibility of the added method or not.
Restricting the visibility makes things quite difficult
> Add extension method to source unit (same locality as static import)
> --------------------------------------------------------------------
>
> Key: GROOVY-11143
> URL: https://issues.apache.org/jira/browse/GROOVY-11143
> Project: Groovy
> Issue Type: New Feature
> Components: groovy-jdk
> Reporter: Eric Milles
> Priority: Major
>
> I have been poking around with the many ways to extend a class/object's
> functionality within groovy. To add a new method that can be called like any
> other instance method, there are a few possibilities:
> 1. modify the MetaClass
> {code:groovy}
> String.metaClass.ext = { ->
> print delegate
> }
> "works".ext()
> {code}
> 2. use a category class
> {code:groovy}
> @Category(String) class Cat {
> void ext() {
> println this
> }
> }
> use (Cat) {
> "works".ext()
> }
> {code}
> 3. apply a mixin
> first create class similar to Cat in (2)
> {code:groovy}
> def str = "works"; str.metaClass.mixin(Cat)
> str.ext()
> {code}
> 4. apply a trait
> {code:groovy}
> trait Ext {
> void ext() { println this.toLowerCase() } // see GROOVY-11142
> }
> "works".withTraits(Ext).ext()
> {code}
> 5. create an extension moodule
> - create class similar to Cat in (2)
> - create META-INF/groovy/org.codehaus.groovy.runtime.ExtensionModule file
> - build and deploy separately from current script / project
> What I'm after is something that works as easily in a script or source file
> as static imports but lets me call like an extension method. And does not
> modify state outside of the current script (like {{MetaClass}}) or introduce
> a thread barrier (like {{use}}). And works with static type checking.
> Scala has an "extension" mechanism that is similar to static import but there
> is a keyword on the category class that lets compiler know the method is used
> like any other instance method. Scala used to provide "implicit" methods --
> I've lost my familiarity with those.
> I've seen "import static extension foo.Bar.baz;" for some language.
> (citation required)
> And lastly, Kotlin provides a local extension like this:
> {code}
> fun foo.Bar.baz() { x ->
> // ...
> }
> {code}
> For any new users or just to add something quickly that can be used in a
> file, I think I'm looking for an enhancement to "import static ..." that will
> get substituted in the source unit, like {{StaticImportVisitor}} does today
> for static method calls. For example:
> {code:groovy}
> import static foo.Bar.baz
> import static /*something*/ foo.Bar.baz
> baz("") // supported by first import
> "".baz() // supported by second import
> {code}
> I have been considering whether "extension", "default", some annotation or
> something else should be used for /\*something\*/ in the script above.
> Similar to Kotlin, this could let someone declare an extension in a single
> script with no dynamic runtime impact:
> {code:groovy}
> import static /*something*/ ThisScript.*
> static ext(String self) {
> print self
> }
> "works".ext()
> {code}
> Has anyone looked at something like this in Groovy or other languages and has
> some feedback?
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