Description Heribert Schütz 2014-02-26 16:14:36 EST

In code like

    if (v instanceof C)
        v.someMethodOfC(...)

the Xtend 2.5 type checker propagates the information that v is an instance of C into the "then" clause of the "if" statement.

It would be nice if this information were propagated in more cases:

*   if (someCondition && v instanceof C && someOtherCondition)
        v.someMethodOfC(...)

*   v instanceof C && v.someBooleanPropertyOfC

*   if (!v instanceof C)
        someExpression
    else
        someCodeExpectingC(v)

*   if (!v instanceof C)
        throw someException // or return;
    someCodeExpectingC(v)

*   if (!(v instanceof C) || v.someBooleanPropertyOfC || !(w instanceof D))
        throw someException
    someCodeExpectingCandD(v, w)

*   if (v instanceof C && v instanceof D) {
        someCodeExpectingC(v)
        someCodeExpectingD(v)
    }

So how far should this go?  I could imagine that the type information may be propagated along the same lines as truth and reachability are propagated by JDT's reachability checker (see also bug #429188), which is stronger than the notion of reachability defined in the Java language spec.