Scott Murphy Heiberg created GROOVY-12602:
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Summary: SC: a lambda in a trait method calling a trait instance
method by implicit this throws ClassCastException: Class cannot be cast to the
trait
Key: GROOVY-12602
URL: https://issues.apache.org/jira/browse/GROOVY-12602
Project: Groovy
Issue Type: Bug
Affects Versions: 5.0.8, 4.0.33, 6.0.0
Reporter: Scott Murphy Heiberg
{code:groovy}
import java.util.function.Supplier
@groovy.transform.CompileStatic
trait U {
String getUname() { 'u' }
String a() { Supplier<String> s = () -> getUname(); s.get() }
}
class C implements U {}
assert new C().a() == 'u'
{code}
Actual:
{noformat}
java.lang.ClassCastException: class java.lang.Class cannot be cast to class U
at U$Trait$Helper$_a_lambda1.doCall(...)
{noformat}
The same happens for a super trait's accessor read as {{uname}} or called as
{{getUname()}} in a lambda, for a lambda in a lambda, for a closure in a lambda
and for a lambda in a trait field initializer.
Expected: the assertion passes, as it does without {{@CompileStatic}}, with
{{@TypeChecked}}, and with a closure instead of the lambda.
A closure in a trait method is rehydrated with the trait instance as its this
object. A statically compiled lambda is not, and the lambda writer passes the
trait helper class as the lambda's this object because the helper method is
static. The implicit-this call then casts that class to the trait.
Seen in 4.0.33, 5.0.8 and 6.0.0.
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