generics - Java 8 and Generalized Target-Type Inference

Question

I have installed the last JDK 8 ea b114 to test the new language features. However the inference in chained calls seems not to work yet.

If I write:

Iterator<String> it = new ArrayList<>().iterator();

the compiler give me an error.

However inference in argument position works well.

Maybe inference in chained calls will not be inserted?

Answer 1

As @Holger said, Java 8 improved contextual inference so that this works_

public static <T> Iterator<T> iter(Iterable<T> i)
{
    return i.iterator();
}

public static void main(String[] args)
{
    Iterator<String> it = iter( new ArrayList<>() );
                \____________________________/
}

It didn't work in Java 7 — the inference on new ArrayList<>() could not depend on context.

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It'll be a huge change to the language to do what you want in the question. John Rose started a similar discussion, see http://mail.openjdk.java.net/pipermail/lambda-dev/2013-July/010531.html

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Too much inference and too much contextual dependency can be a bad thing. It's not so much that the compiler cannot handle the complexity - it can. It's about whether human programmers can handle it. I am sensing that Java 8 is already at a dangerous level that the codes will be difficult for humans to parse.