Methods that return Lambdas Problem

[mortdiggiddy]

Hello,

Great work, truly great.

I noticed a problem when I tried to use this library for the first time. Consider the following code:

public class TestPredicate {
    public static Predicate<Method> withModifiers(int modifier) {
        return m -> m.getModifiers() == modifier;
    }

    public static void main(String[] args){
        Predicate<Method> a = withModifiers(1);
        Class<?> type = TypeResolver.resolveRawArgument(Predicate.class, a.getClass());

        System.out.println(type);
    }
}

Produces console ouput:
class java.lang.Integer

This is wrong, it should produce class java.lang.reflect.Method. I noticed that nested way deep in the code of populateLambdaArgs(...) that it does indeed find a TypeVariable of java.lang.reflect.Method. However this fails the test at the end of the method:

for (int i = 0; i < arguments.length; i++)
    if (paramTypeVars[i + offset] instanceof TypeVariable)
        map.put((TypeVariable<?>) paramTypeVars[i + offset],     
                        arguments[i].getType(lambdaType.getClassLoader()));
             break; 

When the main() method is changed above to this:

public static void main(String[] args){
        Predicate<Method> a = m -> m.getModifiers() == 1;
        Class<?> type = TypeResolver.resolveRawArgument(Predicate.class, a.getClass());

        System.out.println(type);
}

Everything works. class java.lang.reflect.Method

[mickare]

Hi mortdiggiddy! :)

So short story first:
It seems to me that you have a version before the latest commit.
The commit is unfortunately not yet on Maven Central. I'm also waiting on it. ^^

The long version:
I just tested the code on the top with the latest commit and it returned the class Method.
#16

I can tell you how java passes the modifier Integer to the predicate.

In the default use-case of methods, arguments that are passed to a method are in following order: this (if static = null) and then the arguments that are defined in the method header.
In this case it is only Method.

But if you use variables from the outside in a lambda function, Java passes them into the lambda expression by automatically inserting them as arguments behind "this".

The old TypeResolver did not considered that new feature of Java 8.

I hope I could describe a little bit the background story.

So basically in your second code example you don't pass any variables into the lambda expression. That's why it is working.

[jhalterman]

@mortdiggiddy Try the latest release, 0.4.5. This should work as expected in the latest release. Feel free to re-open if this is not the case. Also see the test I added based on your example:

https://github.com/jhalterman/typetools/blob/master/src/test/java/net/jodah/typetools/issues/Issue19.java

[mortdiggiddy]

Good work.