[ nice-Bugs-1624383 ] A case where nullness inference doesn't quite work

Bugs item #1624383, was opened at 2006-12-29 15:11
Message generated for change (Comment added) made by drmaciver
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
Summary: A case where nullness inference doesn't quite work

Initial Comment:
If you do the following, the nullness inference fails unless you add an assertion:

?Foo bar = null;
bar = myMethod();
doStuff(bar);

Where 

public Foo myMethod();
public void doStuff(Foo foo);

The compiler things that foo might be null, and so you can't call doStuff on it. 

At least that's what I think is happening. Here's the sample code which this appeared in:

package kakuro;
import java.util.*;
import java.lang.ref.*;

public class CalculationTable<S, T>
{
    private HashMap<S, ?SoftReference<T>> values = new HashMap();
    private (S -> T) calculate;

    public T get(S arg)
    {
        ?SoftReference<T> valueRef = values.get(arg);
        ?T value;

        if (valueRef == null)
        {
            value = calculate(arg);
        }
        else
        {
            value = valueRef.get();
        }

        if (value == null)
        {
            value = calculate(arg);
            values.put(arg, new SoftReference(value));
        }

        return value;
    }
}

The error occurs with the "new SoftReference(value)".

----------------------------------------------------------------------

Comment By: David R. MacIver (drmaciver)
Date: 2007-01-06 17:02

Message:
Logged In: YES 
user_id=1681313
Originator: NO

And here's a minimal example (I thought I'd tested this example before,
but apparently not):

package nullerror;

public void bug()
{
    ?String value = ""; 
    String otherValue = value;
}


----------------------------------------------------------------------

Comment By: Nobody/Anonymous (nobody)
Date: 2006-12-29 23:17

Message:
Logged In: NO 

Here's a greatly pared down piece of test code:

package test;

public class Test1<S, T>
{
    private (S -> T) calculate;

    public void bug(S arg)
    {
        ?T value = calculate(arg);

        T otherValue = id (value);
        Test2<T> test2 = new Test2(value : value);
    }
}

<T> T id (T arg) = arg;

public class Test2<T>
{
    T value;
}


I've not determined exactly how minimal this is, but it should be pretty
near. Note that the nullness inference fails for both the constructor and
the assignment otherValue = id (value). Also, this does appear to have
something to do with the presence of the type parameters. 



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