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https://issues.apache.org/jira/browse/GROOVY-10699?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17570042#comment-17570042
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Eric Milles commented on GROOVY-10699:
--------------------------------------
It is this bit from {{StaticTypeCheckingSupport}} that gets connections from
{{Function<T,T>}} vs. {{(Double x) -> x}}. At this time, only the return type
is inspected. And in the case of a method call argument, closures/lambdas have
not been visited yet so their return type is unknown.
{code:java}
static void extractGenericsConnections(final Map<GenericsTypeName,
GenericsType> connections, final ClassNode type, final ClassNode target) {
...
} else if (type.equals(CLOSURE_TYPE) && isSAMType(target)) {
// GROOVY-9974, GROOVY-10052: Lambda, Closure, Pointer or Reference
for SAM-type receiver
ClassNode returnType =
StaticTypeCheckingVisitor.wrapTypeIfNecessary(GenericsUtils.parameterizeSAM(target).getV2());
extractGenericsConnections(connections, type.getGenericsTypes(),
new GenericsType[] {returnType.asGenericsType()});
{code}
Next, it is this bit in {{StaticTypeCheckingVisitor}} that was enhanced for
GROOVY-10436 to check for declared parameter types.
{code:java}
protected void inferClosureParameterTypes(final ClassNode receiver, final
Expression arguments, final ClosureExpression expression, final Parameter
target, final MethodNode method) {
...
extractGenericsConnections(gc,
wrapTypeIfNecessary(getType(argument)), pType);
// GROOVY-10436: extract generics connections from
closure parameter declaration(s)
if (argument == expression || (argument instanceof
ClosureExpression && isSAMType(pType))) {
Parameter[] q =
getParametersSafe((ClosureExpression) argument);
ClassNode[] r = extractTypesFromParameters(q); //
maybe typed
ClassNode[] s =
GenericsUtils.parameterizeSAM(pType).getV1();
for (int j = 0; j < r.length && j < s.length; j +=
1)
if (!q[j].isDynamicTyped())
extractGenericsConnections(gc, r[j], s[j]);
}
{code}
It is coming up empty even though it gets [Double] for parameter types (aka
{{r}}).
> Unable to infer type argument from the parameter type of a lambda
> -----------------------------------------------------------------
>
> Key: GROOVY-10699
> URL: https://issues.apache.org/jira/browse/GROOVY-10699
> Project: Groovy
> Issue Type: Bug
> Components: Static Type Checker
> Reporter: Thodoris Sotiropoulos
> Assignee: Eric Milles
> Priority: Major
>
> I have the following program:
> {code}
> import java.util.function.Function;
> import java.util.function.Consumer;
> import java.util.function.Supplier;
> class A<T> {
> A(C<T> x) {}
> }
> class C<T> {
> C(T x ) {}
> }
> class B<X> {
> B(Consumer<X> x) {}
> }
> class D<X> {
> D(Supplier<X> x) {}
> }
> class Test {
> void test() {
> A<String> x = new A<>(new C<>("str")); // type inference works (type
> inferred based on the constant "str")
> D<String> z = new D<>(() -> "fda"); // type inference works (type
> inferred based on the return type of the lambda)
> B<String> y = new B<>((String e) -> {return;} ); // type inference
> doesn't work
> }
> }
> {code}
> h3. Actual behavior
> {code}
> org.codehaus.groovy.control.MultipleCompilationErrorsException: startup
> failed:
> test.groovy: 27: [Static type checking] - Expected type java.lang.Object for
> lambda parameter: e
> @ line 27, column 28.
> B<String> y = new B<>((String e) -> {return;} ); // type inference
> doesn't work
> ^
> 1 error
> {code}
> h3. Expected behavior
> Compile successfully
> Tested against master (commit: 63bcab1bf13fb3811626fb1727c22e86528feb7f)
> **Notes**: As indicated in the accompanying test case, the compiler is unable
> to infer the type argument of a parameterized constructor call from the
> parameter of a lambda, although it works for any other case (including the
> return type of a lambda).
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