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https://issues.apache.org/jira/browse/GROOVY-9971?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17297437#comment-17297437
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Eric Milles commented on GROOVY-9971:
-------------------------------------
I'm not sure what can be done here. The generics check is accurate in that
{{Type<GString>}} is not compatible with {{Type<String>}}. If the method
accepting the closure was a Java method, there would be not chance for
conversion of the return value of the closure.
I have seen test cases like {{List<String> list = ["$x"]}}. When this
assignment was allowed to succeed, the caller of {{list[0]}} would unexpectedly
get a {{GString}} instance, not a {{String}}.
You can change your method to accept {{Closure<? extends CharSequence>}} or
{{Closure<?>}} and always take the {{toString}} of the return value.
> @TypeChecked: Closure<String> no longer compatible with Closure<GString>
> argument
> ---------------------------------------------------------------------------------
>
> Key: GROOVY-9971
> URL: https://issues.apache.org/jira/browse/GROOVY-9971
> Project: Groovy
> Issue Type: Bug
> Components: Compiler
> Affects Versions: 3.0.7
> Environment: Windows 10
> jdk-11.0.10.9-hotspot
> IntelliJ 2020.3.2
> Reporter: mgroovy
> Priority: Major
>
> *Problem*
> A Closure<String> is in Groovy 3 no longer compatible with a closure that
> returns a GString (or String|GString), even though GString is autoconverted
> to String in Groovy.
> *Expected*
> A Closure returning a GString or a String|GString should be compatible with
> Closure<String>
> *Sample Code*
> {code:java}
> import groovy.transform.TypeChecked
> import org.junit.Ignore
> import org.junit.Test
> @TypeChecked
> class Groovy3_ClosureOfString_GString_Compatible {
> @Test @Ignore
> void 'Groovy 3-0-7 Closure with String return type not compatible with
> GString argument'() {
> final x = 123
> // Cannot find matching method
> execStringCls(Closure<groovy.lang.GString>)
> assert execStringCls { "x=$x" } == 'x=123'
> //assert execStringCls { "x=$x".toString() } == 'x=123' //
> works
> }
> @Test @Ignore
> void 'Groovy 3-0-7 Closure with String return type not compatible with
> GString argument 2'() {
> final x = 123
> // Cannot find matching method
> execStringCls(Closure<java.io.Serializable>)
> assert execStringCls { false ? 'abc' : "x=$x" } == 'x=123'
> //assert execStringCls { true ? 'abc' : "x=$x".toString() } ==
> 'x=123' // works
> }
> String execStringCls(Closure<String> cls) {
> cls()
> }
> }
> {code}
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