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Efficiency question about "if()" in PCDs: (was Re: [aspectj-dev] Regular expressions in pointcut expressions) 
Adrian and Cohorts,
A follow up question on efficiency; if you're going to use an "if" test that could either appear in the scope of a PCD or within an advice block, are there rules of thumb for which is better for compilation and runtime performance? (Of course, we shouldn't overlook the "documentation" value of having it in the PCD....) 

For example,

before(): myPCD() && if (someStaticConditionIsTrue()) {
  ...
}

vs.

before(): myPCD() {
  if (someStaticConditionIsTrue()) {
    ...
  }
}

Thanks,
dean

Adrian Colyer wrote:
The pattern matching in AspectJ's pointcut language was deliberately designed not to support regular expressions (too complex and brittle), but only very simple patterns (just * in identifiers). "Programming by regular expressions" is an oft-heard criticism of AOP that I would not be keen to encourage. That part of the language design was settled long before I came on board, and I'm sure Gregor could do a better job than I of explaining the background reasoning that led to that decision. That said, your own example set in context: 

before() : set(* \(*\).\(*\)) && if(exists(* $2.prefix$3(..)) {
  ...
}
does a pretty good job of arguing the case against all on its own to my aesthetic! ;)
The (non-pattern) version of exists can be written today - I suspect a signature along the lines of: 

static boolean exists(JoinPoint.StaticPart,String memberPattern)
would enable you to do most of what you need - heck, memberPattern can even be interpreted using a regex lib if you need it :) 

Then you'd write:

before() : set( ..... ) && if(exists(thisJoinPointStaticPart,"set*(Foo)" {

}

or similar. It's a runtime test of course, so won't work with declare eow.
For the common case of hasMethod and hasField, these *type patterns* have been discussed on the list in an earlier thread, summarized in enhancement request https://bugs.eclipse.org/bugs/show_bug.cgi?id=86818 

-- Adrian
Adrian_Colyer@xxxxxxxxxx


*Dean Wampler <dean@xxxxxxxxxxxxxxxxxxxxx>*
Sent by: aspectj-dev-bounces@xxxxxxxxxxx

11/07/2005 16:54
Please respond to
AspectJ developer discussions <aspectj-dev@xxxxxxxxxxx>


	
To
Alexandre Vasseur <avasseur@xxxxxxxxx>, AspectJ developer discussions <aspectj-dev@xxxxxxxxxxx> 
cc
	
Subject
	Re: [aspectj-dev] Regular expressions in pointcut expressions


	







Alexandre Vasseur wrote:

 >...
 >Perhaps you can reformulate, since it sounds a very bad idea to write
 >something like "set(...) && call(...)" since obviously there won't be
 >any match for that as those are 2 different joinpoint kind.
 >
> > 
Right. I skipped over some details, but basically the intent is to match
the 'set' join points where a corresponding method exists (or in
general, some corresponding condition is met). So, it would be more like
this:

set (* \(*\).\(*\)) && if (exists (* $2.prefix$3(..)))

or something like that. Note that even without the regular expression
stuff, it would nice to have "exists":

set (private Foo.name) && if (exists (* Foo.prefixname(..)))

(Perhaps the "if" is redundant...)

Maybe it would also help to provide a few more details about why this is
interesting for my Contract4J experiments. Currently, the tool has you
define "design by contract" (DbC) tests using expressions in strings
inside special-purpose annotations. E.g.,

@Pre ("n != null")
public void setName (String n) { this.name = n; }

Which defines a "precondition" test that "it's illegal to call setName()
with a null argument."  Currently, rather than embed a runtime
expression interpreter, a precompilation step is done (with Sun's APT -
annotation processing tool) that generates aspects to implement the
tests. So, the string expression gets converted to code, which is then
compiled during the compilation step.

One approach to eliminating the precompilation is to introduce a
JavaBeans-like convention where DbC tests have the same signature as the
methods they advise with a special prefix:

public void setName (String n) { this.name = n; }
public boolean preSetName (String n) { return n != null; }

For an attribute, I could define an invariant test that must always be
true after any change and before any read:

private String name;
public boolean invarName () { return this.name != null; }

So, I would like to write aspects that find these occurrances of  DbC
tests and their corresponding methods or fields and only advise the
methods or fields with before, after, or around advice (as appropriate)
to invoke the test methods.

dean

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Dean Wampler, Ph.D.
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