Question

I have an instance of the object VMemRead (let’s call it r). The constructor for VMemRead looks like

VMemRead(SourcePos sourcePos, VVarRef dest, VMemRef source)

with fields dest and source. I know when I want to access dest, I can just do r.dest. However, I want to go “deeper” into source.

VMRef has two nested classes VMemRef.Global and VMemRef.Stack. VMemRef.Global has the constructor

VMemRef.Global(SourcePos sourcePos, VAddr<VDataSegment> base, int byteOffset)  

I want to access the int byteOffset. In effect, I want to do something like r.source.Global.byteOffset but Java doesn’t let me do this.

Is there any way I can access that value?

Documentation:
VMemRead: http://cs.ucla.edu/classes/spring11/cs132/kannan/vapor-parser/vapor-parser-javadoc/cs132/vapor/ast/VMemRead.html#source

VMemRef: http://cs.ucla.edu/classes/spring11/cs132/kannan/vapor-parser/vapor-parser-javadoc/cs132/vapor/ast/VMemRef.html

VMemRef.Global: http://cs.ucla.edu/classes/spring11/cs132/kannan/vapor-parser/vapor-parser-javadoc/cs132/vapor/ast/VMemRef.Global.html

Thank you very much!

Answer 1

Those nested classes are static. For each of them, you need a reference to an instance in order to access the field values. An instance of VMemRef does not have (documented) member fields of type VMemRef.Global or VMemRef.Stack. You’ll have to look somewhere else than in r for data from those classes.

In other words, simply because you have an instance of VMemRef in r, it doesn’t mean that there are any instances of VMemRef.Global or VMemRef.Stack around. So there’s no way to access “those values” because “those values” don’t necessarily exist!

EDIT After re-reading the API, I see that VMemRef is an abstract class and r.source is an instance of either VMemRef.Global or VMemRef.Static. That changes the story. You can do something like this:

if (r.source instanceof VMemRef.Global) {
    VMemRef.Global source = (VMemRef.Global) r.source;
    // access fields specific to VMemRef.Global
} else if (r.source instanceof VMemRef.Stack) {
    VMemRef.Stack source = (VMemRef.Stack) r.source;
    // access fields specific to VMemRef.Stack
}