@all: Hi again,
@Matthew Wilson: thx for your comments
It is my 5th month now I'm working fulltime on an academic project that is
based on BCEL. The problem discussed here is an important one for me. I try to
solve it, but weeks pass and I'm still not satisfied with the solution. Maybe
you can provide some more comment on this topic in order to propose a better
solution and maybe to better understand the design issue I try to explain.
The design problem is the following.
We have an InstructionList, we want to insert new instructions at certain
points. We are using a visitor class implementing the visitor interface to
visit the whole instruction list and do the changes to it.
Let's say our loop over the InstructionList is in a class A, our Visitor is
class B.
In A the loop looks the following:
for(InstructionHandle currIH: iList.getInstructionHandles() )
{
currIH.accept(instanceOfVisitorClassB);
}
one certain method in the( visitor ) class B looks something like this:
public void visitASTORE( ASTORE obj ) {
...
InstructionList il = new InstructionList();
... // fill the new il
// insert instructions before actual ASTORE instruction
iList.insert( obj, il );
iList.setPositions();
super.visitASTORE( obj );
}
So if the ASTORE instruction is visited we call the method
insert(Instruction, InstructionList) which causes the error described before
(insertion point may be wrong because of == equal refrence match on
instructions).
Therefore we shouldn't visit the INSTRUCTIONS but the INSTRUCTIONHANDLES but as
far as I know there isnt' a visitor which has the interface
visitASTORE( ASTOREHANDLE obj ) or something like that.
My dirty, quickfix, hack is the following:
Class B I put as inner class into A, the loop in class A sets a public field
currentVisitedInstructionHandle, then the visitor method I changed to:
public void visitASTORE( ASTORE obj ) {
...
// insert instructions before actual ASTORE instruction
_textsegment_il.insert( currentVisitedInstructionHandle, il );
_textsegment_il.setPositions();
}
THE DIFFERENCE IS:
insert(InstructionHandle, InstructionList) is called, and because
InstructionHandles are unique our insertion is correct.
NOW: I think this is somehow ugly, right?
I tried to write an InstructionHandle visitor, I already wrapped all the
Instruction class automatically, but then I realized that it is far too much
work for one guy.
Do you see my point? I think the design of the visitor (which is a great
concept!) should be somehow changed to better address a problem like that.
If you have any better solution, or if I'm doing something wrong, please let me
now!
@Matthew: do you have an idea?
kind regards
zagi
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