Scott Murphy Heiberg created GROOVY-12623:
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Summary: SC: a method reference to a generic method used for a
primitive SAM return type (e.g. Predicate) throws ClassCastException instead of
applying Groovy truth
Key: GROOVY-12623
URL: https://issues.apache.org/jira/browse/GROOVY-12623
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.Predicate
@groovy.transform.CompileStatic
class C {
static <T> T id(T t) { t }
static void main(args) {
Predicate<String> p = C::id
assert [p.test(''), p.test('x')] == [false, true]
}
}
{code}
Actual: {{java.lang.ClassCastException: class java.lang.String cannot be cast
to class java.lang.Boolean}} at {{p.test('x')}}. The same happens for the get
method of a Map of String to String used as a Predicate (bound or unbound),
List::first, an Optional's get as a BooleanSupplier, and generic instance
methods. For numeric SAMs, a ToIntFunction of String or Character with
{{C::id}} gives "cannot be cast to class java.lang.Number".
Expected: [false, true], as in dynamic Groovy and under @TypeChecked; 120 and
65 for the numeric cases.
When the referenced method returns a type parameter, the static compiler sets
the instantiated return type to the SAM's wrapper type (GROOVY-10975) and
leaves the conversion to LambdaMetafactory, which only casts and unboxes.
Seen in 4.0.33, 5.0.8 and 6.0.0.
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