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https://issues.apache.org/jira/browse/GROOVY-12617?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Paul King resolved GROOVY-12617.
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Fix Version/s: 7.0.0-alpha-1
Assignee: Paul King
Resolution: Fixed
> SC: a method reference to a functional interface with a primitive return type
> fails at bootstrap when the return value needs a Groovy conversion (e.g.
> String to boolean)
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: GROOVY-12617
> URL: https://issues.apache.org/jira/browse/GROOVY-12617
> Project: Groovy
> Issue Type: Bug
> Affects Versions: 4.0.33, 5.0.8, 6.0.0
> Reporter: Scott Murphy Heiberg
> Assignee: Paul King
> Priority: Major
> Fix For: 7.0.0-alpha-1
>
>
> {code:groovy}
> import java.util.function.Predicate
> @groovy.transform.CompileStatic
> class C {
> static String str(String s) { s }
> static void main(args) {
> Predicate<String> p = C::str
> assert !p.test('') && p.test('x')
> }
> }
> {code}
> Actual: the code compiles, but evaluating the method reference throws
> {{java.lang.BootstrapMethodError}}, caused by
> {{java.lang.invoke.LambdaConversionException: Type mismatch for lambda
> expected return: class java.lang.String is not convertible to boolean}}. The
> same happens for every primitive return that the type checker accepts but the
> JVM cannot convert: boolean from any reference type or from int,
> ToDoubleFunction from a BigDecimal method, and ToIntFunction from a long or
> Long method.
> Expected: the value is converted as in dynamic Groovy, @TypeChecked code and
> a method pointer ({{C.&str}}), which all give [false, true] here (Groovy
> truth).
> Cause: the static compiler binds the method directly through
> LambdaMetafactory, which converts a return value to a primitive type only by
> unboxing and widening primitive conversion.
> Seen in 4.0.33, 5.0.8 and 6.0.0.
> PR: https://github.com/apache/groovy/pull/3143
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