Aspect-Oriented Programming Considered Harmful 470
kupci writes "The 'x considered harmful' cry is a little overused, but there is a Forrester report that discusses some of the pro's and con's of Aspect-oriented Programming, and includes some interesting links. It is mainly based on papers from the University of Passau. It's worth it just for Clark's 'COME FROM' article." From the article: "Aspect-oriented programming (AOP) is intended to address common problems that object-oriented programming (OOP) doesn't address well, plus some problems that OOP itself created. However, AOP is a risky solution: It is a very generic mechanism for solving some very specific concerns and has been likened to a kind of "GOTO" statement for OOP. Like GOTO, it can cause more harm than good."
Of course (Score:5, Funny)
I happen to LIKE C++! (Score:2, Insightful)
classic newbie blunder (Score:5, Funny)
You've attempted to assign C++ to a complex left-hand-side expression (GOTO+OOP). This is a classic blunder. What you probably meant was: "GOTO"+"OOP" == "C++".
In addition, you're overloading the use of strings to have orthogonal meanings, which is frowned upon. After all, using the standard string operator overloading, your left-hand-side "GOTO"+"OOP" is simply "GOTOOOP", which is clearly not equal to "C++" -- a good comment compiler would notify you that this expression always evaluates to false. A further refinement would be to introduce your own class and write the expression as:
LanguageFeature("GOTO")+LanguageFeature("OOP") == LanguageFeature("C++").
In the future, I hope slashdot will provide a better comment compiler that can automatically detect such simple mistakes.
Re:Let's not forget (Score:2)
Re:Of course (Score:3, Informative)
Quick! Somebody start a petition to demand that Intel drop the JMP instruction from its processors! It's an abomination!
Re:Of course (Score:4, Insightful)
Re:Of course (Score:3, Informative)
And? High level languages have immediate targetted transfer of control instructions as well that one cannot easily get rid of. For example, C has break, continue, and the closing squiggles of for and while statements.
"High" level languages makes programmers not as aware as they should be when they're moving a different value into the instruction pointer, but their programs are still doing precisely that at various points.
One could argue that C an
Re:Of course (Score:4, Insightful)
But all of those statements are used in the context of some logical block, and in some sense "operate" on that block. GOTO is/does not - in C/C++, at least, the only restriction is that you must GOTO a label that's in scope at the time.
"High" level languages makes programmers not as aware as they should be when they're moving a different value into the instruction pointer,
High level languages also relieve the programmer of the need of thinking about things like stack frames, heap management, and register usage. A programmer should in a general sense understand how these things work, but there doesn't need to be a constant awareness of those factors, because the compiler is designed to take care of them instead. Programmers working on hardcore optimization might have an interest in those low-level details, but a good optimizing compiler will take care of most of that before the programmer even starts to think about optimization.
The point in my original comment was that, in assembler, not using JMP reminds one of, "You can't get very far in life without saying 'is'". But the last time I've needed a GOTO was when I was a teenager naively programming in BASIC on my old C-64.
Re:Of course (Score:3, Interesting)
Indeed, and now inheritance and polymorphism are probably the most over-used programming language features on the planet.
I'm not saying you're wrong to try to isolate self-contained and independent blocks of code -- you're not -- I'm just saying that it's not
For those unfamiliar with AOP (Score:5, Informative)
In computing, the programming paradigm of aspect-oriented programming (AOP) centers on constructs called aspects, which treat concerns of objects, classes, or methods. The aim of AOP is to separate program code related to the main purposes of the application (its core concerns) from code related to secondary purposes (cross-cutting concerns).
For example, a telecommunications application might have a core concern of routing calls, while code for timing and billing those calls would crosscut the whole object hierarchy. AOP aims to separate the billing concerns from the core concern. It moves code not related to solving the domain problem from the business logic into a separate module. The application code no longer contains pieces of crosscutting concerns scattered across modules; instead, programmers maintain crosscutting concerns in aspects; this makes it easier to maintain both core and crosscutting concerns.
Any program has principled points (join points) where programmers can identify and modify the program semantics. In AOP, programmers specify join points using a language feature called a pointcut, and specify the behavior to join those points by using advice such as methods or functions. Some variants of AOP allow programmers to extend the types in the system. These features enable aspects to implement behavior for concerns that crosscut the core concern of the application.
Re:For those unfamiliar with AOP (Score:5, Insightful)
Excuse me, but was that supposed to mean something?
Re:For those unfamiliar with AOP (Score:5, Insightful)
Objects a and b do something useful (the core of the application)
Object c (an aspect) wants to perform an operation when something happens in object a (a concern).
Object c (an asepct) also wants to do different things when something happens in object a and b (crosscutting a concern).
I look at this as a really complicated event notification system. Comments calling this 'goto for OOP' also seems rather appropriate.
Re:Where are all the aspect gurus? (Score:4, Informative)
We were doing a compiler in that project and that was a very good time to use AOP. From the CC programs you get a bunch of object code, but you don't want to edit these files as they are generated by other programs. Instead we used aspects which are then "weaved" into the generated code (this is what is called joints and concerns now). In reality it's pretty much a bunch of pre-compiler steps.
Eg we did an Aspect of the compiler code called Interpret. This aspect added a method "interpret()" in all classes, and you can easily define it's default behaviour as well as adding specific behaviours for some classes. So in our case we defined expressions to return their values and print statements to do a println and so on.
Run the pre-compiler steps, then compile and you've got a compiler that can parse and interpret code. Now add a new stamtement type to the grammar, and do it again and you have a new compiler working. No need to hand edit a bunch of files.
Naturally since this was in the early stages one problem was that looking for compiler errors in generated code was a bit of a bother. All in all it was a great help.
Re:For those unfamiliar with AOP (Score:5, Informative)
The whole idea of AOP is that it's not a GOTO. The "interceptor" (or whatever the jargon of the week is) gets called, does its thing, returns, and your original function runs. This is nothing, lisp does this with defadvice, even emacs lisp can do this (and indeed emacs lisp makes good use of it).
The neat thing about aspects is that you define them in ONE place. So you tell it "I want function setup_db_connection() and teardown_db_connection() called before every method on any Person, Room, and Resource" (imagine it's a scheduling app). This is just like subclassing, but you don't have to rewrite anything else in the app. In fact, VB programmers who did this sort of hook trickery actually did call it subclassing. If you use a factory pattern, you can do this sort of thing without AOP, but the idea of AOP is to not force you to rewrite everything to use factory patterns -- you just define the "aspect" once, in one place, and it affects everything you tell it to.
I find AOP is a great way to impose "external" conditions like debugging, extra asserts, and tests. I don't think it's necessarily a great way to structure an entire program, though someone with more experience in the methodology might make it work. As a new methodology, it's rife with shoddy implementations, buzzwords, overuse, poor use, and general immaturity. This is how all methodologies start out however -- even structured programming went overboard when it was first introduced to the mainstream.
Re: (Score:2, Interesting)
Re:For those unfamiliar with AOP (Score:2)
Re:For those unfamiliar with AOP (Score:3, Insightful)
Re:For those unfamiliar with AOP (Score:4, Insightful)
A better example might be a computerized patient record system (CPRS).
In a CPRS, it is clear that the core concerns involve information related to the patient's health. However if the institution is going to stay in business, there is a strong secondary concern with regard to diagnosis and treatment costs, billing, and so on. Obviously a healthy hospital has to deal with both of these.
AOP's promise in this situation is to allow these two mission-critical concerns to be temporarily divorced from each other, so that in a medical emergency the patient will get the treatment he needs in a timely way, without doctors and nurses having to deal with billing and cost issues (Clippy: "It looks like you want to defibrillate the patient. Would you like me to compare the costs of alternate treatment modalities?")
I've not run into this "AOP" thingee before. My impression is that the problems it is supposed to solve would be better approached by a change in the object hierarchy-- that its use would be sort of like adding epicycles to epicycles when a Copernican revolution is really needed. In the CPRS example, rather than having a PATIENT object with healthcare and billing concerns, it might work better to have TREATMENT and BILLING objects that were separate components of the PATIENT object.
I'm not convinced that the problems AOP is intended to solve couldn't be finessed by refactoring into a different hierarchy of objects.
$249 (Score:4, Interesting)
Re:$249 (Score:3, Interesting)
Re:$249 (Score:2, Funny)
Oh gee (Score:5, Interesting)
Thank you for the wonderful advice and welcome to 1971!!
As for the GOTO comparison, it is disingenuous. The problem with GOTO is not that it is a flow control change, the problem is that it is an [i]unstructured[/i] flow control change. AOP is nothing if not structured, in fact its potential flaw lies in that the structures it represents can be so complicated the programmer can lose track. It's the absolute opposite of GOTO.
Re:Oh gee (Score:2)
Re:Oh gee (Score:5, Insightful)
To quote: "... it becomes terribly hard to find a meaningful set of coordinates in which to describe the process progress
I think Dijkstra's point was that any construct that does this is harmful.
Structured constructs are typically less liable to do this, but only because they are visible and the structure is known.
AOP does have the ability to inject arbitrary code in your function that can change its semantics and you cannot see this when reading the affected code.
No matter how structured that change is, its invisibility makes it impossible to fully understand your code from the source code without 'weaving in' all the aspects explicitly. Like GOTO, it destroys your ability to scope your reasoning of the code to the local view.
As much as I love AOP for a class of problems, this is a very valid concern that needs to be addressed.
It's certainly not the first language featureset that faces this problem; OOP can deal with its own issues with design by contract, either through documented best practices or by enforcing it in the language. I haven't seen much in AOP there, beyond the absence of problematic examples (which would typically come from real-world use).
Re:Oh gee (Score:3, Insightful)
Well, except that AOP can only modify code in a structured way.. You can replace a method (no more obscure than method over-loading), you can wrap a method, turning it's body into a nested scope (again similar to a method which calls super). Yes they have before and after methods, but these are mere conviniences to the wrapping of a method.
My argument i
Considered... Harmful? (Score:3, Funny)
Re:Considered... Harmful? (Score:2)
NEWS FLASH (Score:4, Funny)
Re:NEWS FLASH (Score:2)
Angry Flower (Score:3, Funny)
Re:Angry Flower (Score:3, Funny)
A bit sketchy to be called an article (Score:4, Informative)
Executive Whining (Score:5, Insightful)
Re:Executive Whining (Score:2)
With goto you're branching to a specific label.
With Aspects you're doing dynamic wildcard modifications of code based on procedure names!
If that wasn't horrifying enough, it also circumvents the compiler (or interpreter)'s error checking.
This is even scarier and less controllable than old COBOL self-modifying code feature
(the much reviled ALTER X TO PROCEED TO Y
long since removed from the language.
I'm missing something. (Score:2, Insightful)
So how can AOP be like GOTO for OOP when GOTO is already the GOTO for OOP?
LK
It's not considered in the context of OOP (Score:4, Funny)
I like GOTO! (Score:5, Insightful)
I like GOTOs. GOTO has it's place. Even in C++. Sorry all you purists, but there are times when it just plain works.
*runs and puts on Chinese wicker fighting suit and hides, trembling, behind a flame-retardant wall*
Re:I like GOTO! (Score:2)
GOTO statements are *BAD*, I had been taught. But there are places, I had to use it. Being hardcore fan of OO... I hated it. But no options.
There are more shocks you see when u switch languages. Had big pains to implement frameworks in C++ while keeping options of callbacks. (If somebody knows, I will appreciate it) But I was shocked to see that CALLBACKS were put down by C++ purists, which is so com
Re:I like GOTO! (Score:3, Interesting)
???
Callbacks are everywhere in C++ although these days they are often function objects instead of function pointers. Somebody who puts down callbacks is certainly no C++ purist.
Re:I like GOTO! (Score:4, Informative)
Sure. This is an example using the boost::function and boost::bind libraries which have both been available for a long time and are in the process of becoming part of the standard C++ library.If you don't want to use libraries just assign function objects or static class functions.
If you want to do several callbacks at once check out one of the many available signal/slot libraries.
Re:I like GOTO! (Score:4, Insightful)
Well, callbacks are a fairly straightforward concept. They're most commonly used in things like GUI programming, where you do a lot of (asynchronous) event handling.
But more generally, callbacks are just a very specific example of functional programming, which is just another style of programming that emphasises functions as first-class elements. And because C++ supports several programming paradigms, you can do object-oriented programming, functional programming and/or generic programming - often all at the same time.
Just like in Perl, there's more than one way to do it. And there isn't any one "correct" way - whatever gets the job done is fine.
No.
Object-oriented programming is widely recognised as first being implemented on a language called Simula [wikipedia.org] in the 1960s. 1962 [ifi.uio.no] to be precise - for Simula I - though Bjarne Stroustrup based C++ most closely on the OO concepts in Simula 67 (1967).
Pascal was first implemented in 1970 [wikipedia.org], though the original Pascal didn't support object-oriented programming.
I'm not quite sure what you mean by that. Most implementations of Pascal don't support object-oriented programming at all, much less have "inherent capability". Those implementations that do support OO-style programming usually aren't called Pascal - eg. Delphi, Oberon, Modula-2.
You're using your terminology confusingly here, so it's difficult to work out exactly what you're saying. But I can say that I've only seen a few occasions where it'd be useful to work out if Base* p is actually pointing at a Derived object, and usually those cases arise when you've started out with a bad design or bad logic. Usually the whole point of having a (pointer-to) Base is that you're supposed to rely on using Base functionality. You're not supposed to care if it might actually be a Derived, the only thing that should matter is that it is substitutable-for [parashift.com] a Base. If you need to access Derived functionality, you should have a Derived.
But anyway, in those cases where you're dealing with someone else's badly designed code, a dynamic_cast should be enough to get around it. Take your Base* and try to dynamic_cast it to a Derived* - if that fails, you haven't got a valid pointer-to-Derived. Go find the person that built the code you're using and kick them. Hard. :-)
Re:I like GOTO! (Score:4, Informative)
Ok, here you go:All standard C++, using the C++ standard library. And also it's all genuine C++ code, not just C code moved to C++.
I don't know what it gives you, but here you are:I'm of course assuming that callback and f are of compatible types.
Why? If you haven't yet found out, C++ is not a pure object-oriented language, but a multi-paradigm language. The code I've shown actually uses generic programming (ok, it just scratches at the surface of GP, since it only uses the STL algorithms, but doesn't define one on it's own).
But then, if you want a typical OO version of callback, just look up the observer pattern. (And no, I'm not going to show that here as well, it's already hard enough to get the above code through Slashdot's lame[ness] filter!)
Well, in the example above, I've had only 3 C global functions: is_negative (but this would probably be better done with standard function objects and binding anyway), std::sqrt (the standard library just has this as function, but it could be encapsulated as object as well), and main (whiuch you just cannot avoid in C++ anyway). The rest are either function templates or objects (which is typical for generic programming).
Re:I like GOTO! (Score:5, Informative)
It is also exceedingly useful for error handling, in that it allows you to skip the bulk of a function and still hit the cleanup section of the function. This gives you two things:
1) you avoid a deep, deep mess of nested if statements
2) you eliminate duplication of code in error handlers (and the bugs that occur later on when someone forgot to update one of those handlers to release some resource they just added)
Re:I like GOTO! (Score:3, Interesting)
Re:I like GOTO! (Score:3, Interesting)
While anything allocated on the stack will be destroyed when an exception is thrown, any resources allocated during execution will leak (ex: handles or memory allocated on the heap). As the data on the stack is deallocated (the very items which were referencing the afore mentioned resources), you never get an opportunity to clean up after the error condition. To make matters worse, you never get an opportunity to rol
Re:I like GOTO! (Score:3, Informative)
While anything allocated on the stack will be destroyed when an exception is thrown, any resources allocated during execution will leak (ex: handles or memory allocated on the heap).
Wow, this is stunningly wrong. That's what destructors are for - they will free any resources that your local objects allocated/acquired. That's the resource acquisition is initialisation [att.com] paradigm, and it ensures that resources are always freed when you leave a scope. This is contrary to using a goto for error handling,
Re:I like GOTO! (Score:3, Insightful)
void MyFunction()
{
char *szString = new char[25];
if (somethingfailed)
return;
delete [] szString;
}
szString leaks.
Now, that can be modified as follows:
void MyFunction()
{
char *szString = new char[25];
if (somethingfailed)
{
delete [] szString;
return;
}
delete [] szString;
}
Now imagine you've got 20 "somethingfailed" type conditions in your method.
Frankly there ought to be more goto in C (Score:2)
C-- (Score:2)
The absence of "goto myfunc(param);" makes implementing coroutines or tail calls un-necessarily hard when using C (or compiling to C).
If your C compiler does not optimize obvious tail calls (e.g. return myfunc(param);), then your C compiler has a bug.
There is no valid reason for a very-low-level language to hide features available from assembler.
C is not a very low level language. You're thinking of C-- [cminusminus.org].
Re:I like GOTO! (Score:3, Interesting)
Yes it works, but it's not clean. The only reason I use gotos in c/c++ code is to break out of multiple levels of scope or for a basic 'goto end' pattern in a long/complex routine that needs to ensure cleanup before returning. I suppose I'd also use it
Re:I like GOTO! (Score:5, Interesting)
void foo()
{
do some thing
if(error)
goto err1;
do something more;
if(error)
goto err2;
return;
err2:
free stuff
err1:
free more stuff
}
For anything else I shun goto.
Re:I like GOTO! (Score:5, Insightful)
Exceptions incur an obscene performance hit, and should be used for 'exceptional' conditions and not expected/handled errors. You also have to worry about the case where someone else adds another exception handler that inadvertantly 'catches' your thrown exception (which makes for maintainance problems later down the road).
Re:I like GOTO! (Score:4, Insightful)
Re:I like GOTO! (Score:5, Informative)
The freeing of resources, all resources not just memory, is automatic in C++ once you learn to use RAII.
Look it up. It is one of major improvements of standard C++ over C/C++.
Re:I like GOTO! (Score:3, Interesting)
And in the process your code just got a lot more complicated. Because now you use RAII in some places, and hand coding in other places. It gets worse if you do both in the same function, as then there is a large amount of confusion about when, where, and how certain resources are being removed. And don't
Re:I like GOTO! (Score:3, Informative)
Of course, check out http://c2.com/cgi/wiki?ResourceAcquisitionIsIniti
it works perfectly well in C.
How does it work without destructors?
Re:I like GOTO! (Score:3, Interesting)
A function longer than a screenfull is too long, I never have such.
Re:I like GOTO! (Score:3, Interesting)
FOO: for(..) {
BAR: for (..) {
if (..)
continue FOO;
if (..)
break BAR;
Perl was nice because it had even more flow-control statements
Re:I like GOTO! (Score:3, Informative)
Re:I like GOTO! (Score:2)
You can replace "string" with any other form of buffered deterministic input parsing.
Re:I like GOTO! (Score:2)
If you have TWO conditions to one specific code sequence where 2nd test *CAN* cause pagefaults if first test do not pass. The said code sequence is such that creating a separate function for it is out of question and replicating the sequence inside elseif would be just another place to fix problems. So I go for short goto sequences.
Like contion1 is something like if pointer=null or arrayindex=-1 or something similar.
Yes the arrayIndex=-1 while accessing array CAN cause pagefaults. Get
best tool for the task (Score:5, Interesting)
Log.printLog("some message " + someObject.toString());
everywhere you want to log something. But with AOP you can used kleen operators (*, +, ?, etc) to add Log.printLog() to certain methods of certain objects. Aspects allow you to inject code into method call boundaries. But like all programming constructs it can be abused. This is because you might get an exception stack trace that indicates a specific method call has thrown an exception when the exception came from code inserted by an aspect. But other languages can be abused too (Perl anyone). So I think this type of critism of aspects says more about the critic than about the programming construct. I don't use C++ to implement logic evaluators (I would use Prolog or another logic or unification based language). Nor do I try to write OO code in LISP (despite the horrid OO extensions for LISP) because each language has it strengths and weaknesses. For each application choose the language that best suites the task.
On another note, I think these types of critisms are really from people who are afraid of learning new languages or skills. They have worked long and hard to get good at C (or Java or some other language) and don't want to have to learn another language. Well suck it up, there aren't many Fortran programmers anymore and if you want to keep working, you must keep learning new languages and skills. Not that you should jump on every bandwagon, but if I'm writing something that needs to be really, really fast I use C. If I'm writing something that needs to be maintainable forever and speed isn't that important I use Java. The best tool for the task.
Re:best tool for the task (Score:2)
Log.printLog("some message " + someObject.toString());
not:
Log "some message " someObject endl;
???
-a
Re:best tool for the task (Score:2)
Log << "some message " << someObject << endl;
Re:best tool for the task (Score:3, Informative)
2)Even in C++ a lot of people avoid that usage. Its an example of everything thats wrong with operator overloading. ab means left shift a by b bits. Overriding it to now mean write to a stream is a horrible and confusing idea. Would you override + to mean something totally different than addition?
Re:best tool for the task (Score:2)
"a << b means left shift a by b bits"
Re:best tool for the task (Score:2, Interesting)
But what does AOP solve in that logging scenario? As far as I can tell, it lets you change this:
Into this:
Four less characters, whoop-di-shit.
And that's not even going into the fact that static import brings exactly the same benefit.
Re:best tool for the task (Score:3, Insightful)
Re:best tool for the task (Score:2)
Re:best tool for the task (Score:3, Insightful)
The concern predates the report for quite a bit, and from some reliable sources. This is not a surprise, as I would think the role of companies like forrester is to communicate trends like these, not to create them out of the b
Re:best tool for the task (Score:3, Insightful)
if you don't try to write OO code in lisp, how do you know it cannot be done (and done well)?
hint: AOP is just half-assed CLOS.
(no worries, i don't use any of this stuff, either. ;-)
Re:best tool for the task (Score:3, Insightful)
I think that, a priori, we should read criticism as an opportunity to improve concepts, not merel
$250 to read the article (Score:3, Informative)
'It's worth it'. Come on, how many people here read the article, let alone will pay $250 for it?
Re:$250 to read the article (Score:2)
Re:$250 to read the article (Score:2)
It's not a viable programming technique, but it's a viable method for siphoning money into their account. And as thus, a valid business method.
Buy this document? 249.00??? (Score:4, Insightful)
What bollocks.
Do any CIOs still buy this crap? Do the sensationalist headlines do the job and actually sell this bs? "AOP considered harmful"...be afraid...be very afraid!
I personally don't have a week go by when we don't find another great use for AOP...and we write financial apps...so that blows his 'frameworks only' theory out of the water.
But I suppose "AOP, useful sometimes in the right circumstances if you make sure you train your people on how to use it, not so useful in others" doesn't exactly sell those $250 a pop articles, does it Carl
Patented (Score:2)
Side effects++ (Score:5, Insightful)
Functional programming: f(1) == f(1) always, with no other effects to "global state" etc.
Imperative programming without AOP: f(1) != f(1) necessarily at every point of the code, as the function can access globals. It can also change the global state, so its effect is more than returning its value; it can have side effets.
Imperative programming with AOP: Same as above, plus the side effects may happen somewhere unrelated to the definition of f itself.
Re:Side effects++ (Score:2)
Re:Side effects++ (Score:2, Interesting)
What haskell infact lets you do with its IO monad is construct instructions for a separate IO interpreter (that is not pure) within the Haskell runtime. It is a kind of DSL (domain-specific language), a concept that is used a
DSL? (Score:2, Funny)
What haskell infact lets you do with its IO monad is construct instructions for a separate IO interpreter (that is not pure) within the Haskell runtime. It is a kind of DSL (domain-specific language), a concept that is used a lot in Haskell programs.
Then what are the impure languages? Dial-up?
10 GOTO 10 (Score:3, Interesting)
Forrester is just another clueless IT consultancy (Score:5, Insightful)
These consultancies ran out of ideas a long time ago, and are trying to turn IT ito some Six Sigma pseudo-science. It doesn't work, but idiots still buy into it because it sounds impressive.
$50 per copied page??? (Score:3, Interesting)
How do I get suckers^H^H^H^H^H^H^Hfolks to pay $250 for my 5 page speculations on computer science topics? Seriously. I'm an academic, and I write 20+ pages per month of this stuff for free. If I could get even 100 people to pay $50 per page each for it, that would be $100K per month: that's way more than I make in a year at my current job. Leaving aside the question of the price of my immortal soul, it doesn't sound like too bad a gig.
I started to list my qualifications, but got tired of typing. Suffice it to say that they're way more than that Forrester guy has. Let me know folks: if 100 of you pay me $50 per page each, I'll research pretty much whatever you want.
Very true. That's what i told them at IBM HRL (Score:4, Interesting)
The concepts behind AspectJ, TMO, are not bright. They break encapsulation, they are too ambitious and far from real-world understanding of programming concerns. All in all, they introduce too many problems.
TMHO,Aspect Oriented Programming should be different, and should be based on something much simpler, much more down-to-earth ideas and more consistent with real-world needs.
Today it is easily possible to do using Java Annotations, that will specify class member's affinity with an aspect, and thus provide:
A) a mechanism by which the compiler could limit access (errors & warnings) to members according to their affinity with a common aspect or aspects (common to it and its caller);
B) a programmer, using a proper IDE, can view a breakdown of his code according to aspects.
C) in runtime, the current aspect should be visible to the program thus extending the ability to: I) log, and trace errors; II) affect work-flow according to the aspect in action (that's an intense feature so im not too sure about that)
Doing more than the above, looks to be like an abuse of proper programming concepts.
The Annotation mechanism introduced in Java 5 is quite powerful and maybe already provide all that is needed for the job, including hierarchical arrangement of aspects (slash annotations), attributes, etc. Very little is needed in order to implement what i propose.
Maybe i'll propose is to the JCP. What'd ya think?
Quite confused (Score:3, Interesting)
AOP basically means that when an object is created, or a method is called you wan't to run some code?
So if we tried to put this into a non-OOP example you would basically be calling something else whenever certain functions were called? Eg calling a 'save', 'load' or 'start' function would result in running the 'logging' function too?
But as I gather (and its pretty hard to find a simple explanation around here) the idea of AOP is that it allows you to do this without having to put any function calls in your code, ie it 'captures events'. So if for example you had to implement some security checks but you were worried that someone in your project would forget to put the 'if(secure)' lines into their modules you could rest assured that AOP would be on the case.
Then theres COME FROM which is basically an event handler that says 'when you get to this line/label in your code, come over here and run me.
I see no problem with this in a relatively high-level environment where the goal is to write less code and where so much crap is going on in the background anyway (dynamic this and managed that) that another overlay is just going to make things look simpler.
Isn't this however almost exactly the same as an interrupt?
To paraphrase Mr Heston... (Score:2, Insightful)
All these arguments about different methodologies and techniques being harmful or not boil down to one thing:
"There are no good constructs, there are no bad constructs; a compiler in the hands of a bad programmer is a bad thing, a compiler in the hands of a good programmer is no threat to anyone - except the patent system."Software Patents Considered Harmful (Score:5, Interesting)
So, who really cares if its theoretically any good, when legally it is worthless?
AOP sound in principle (Score:5, Interesting)
I've been following AOP (cautiously) for some years now. Here's a few salient points for those who don't have $250 to splash out.
The underlying principle of AOP is about "separation of concerns", a term introduced by Dijkstra back in 1974. Separation of concerns is a Good Thing[tm], but there's more than one way to do it. It's a conceptual thing more than it is any one particular implementation technique.
Both structured and OO programming offer techniques that allow the hacker to more clearly separate concerns: by organising their code into subroutines, modules, objects, methods and so on. The problem with OOP is that real world problems don't always break down into a set of clearly defined, independant object classes. In some cases you can end up with a problem fragmented into so many small pieces that you can no longer see the wood for the trees.
AOP tries to address this by allowing you to identify those concerns that don't fit neatly into an object model. These "cross-cutting" concerns are typically things like logging, debugging and security that affect many of the objects in your system. If you decide to change the way logging is handled, for example, you don't want to have to go and edit every single object that generates logging information. But that's often what happens in OO based systems - you design your class hierarchy with Products, Customers, Orders and other real-world entities in mind and implement them as "black-boxes" with internal functionality neatly hidden away. That's fine when the functionality really is local to the object, but not when it relates to a system-wide aspect like logging, etc. These are the kind of undesirable artifacts that can arise from the decomposition of a problem into objects.
However, that's not to say that there aren't ways of achieving the good parts of AOP in a non-AOP language. Many Design Patterns are examples of separating concerns. The Model/View/Controller and Model/Visitor patterns come immediately to mind. Going back to the early logging example, we could implement this in AOP fashion in an OO language, by creating a "Logger" object which implements all the logging functionality. Just make sure all your other objects delegate to the logger for logging rather than trying to do it themselves. Now you have all your logging code in one place, and you just have to worry about how you're going to pass the logger object around so that all your other objects can call on it... (and this is often the start of the rest of the problems...)
So AOP-a-like can be done in OO languages, but most OO languages aren't really cut out for it - you have to code the magic manually if you want it. Hence the rise of AOP languages (usually just bolt-on syntax additions to existing languages) that make this process that little bit easier.
AOP in Java does smell a little like GOTO, IMHO. In brief, it uses "join points" to connect different aspects together (e.g. call this logging method just before calling that other method). One can certainly argue that it's a more structured form of GOTO, but I believe the same fundamental problems remain: control flow jumping all over the place, with actions-at-a-distance waiting to catch out the unsuspecting programmer.
So my advice on AOP would be to treat it like OOP, XML, Java, and all the other "silver bullets" that over the years have claimed to be the next big thing that will save our collective software sanity. Recognise the problem that it's trying to solve, realise the benefits of the particular solution(s) presented, and ignore all the hype!
Objective-C has these, and no one bats an eyelash. (Score:5, Informative)
First it has categories, which allow you to add new methods, or replace the implementation of a method in a given class. You add a category to that class that includes, say, a replacement description method, and the new implementation replaces the old. Or you can add a path utility methods to the String class, as another example.
It also has "poseAs", which allows you to insert an object into a hierarchy. Say you have Class B which extends Class A. But you want custom behaviour to be accessible to all As children (including, for example, B). You create Class C, which extends A, and make it poseAs Class A. Now the runtime hooks all clesses that inherit A off of C, which replaces A. A still exists, but is in the background, providing normal inherited functionality to C.
These abilities were one of the things that made Objective C a very powerful OO language. In particular, it allows a particular kind of reuse, by virtue of allowing one to patch someone else's library without having source. So if you want to add the aforementioned path utilities to NSString, you just added a Category in your own code, and your code would run with the extended functionality in NSString (no one elses would, unless they used your category too). This means that often you can make the most out of someone else's code without a complete rewrite.
It isn't all powerful. There are access and visibility restrictions. It is also used to partition code for ease of organization and better modularization. Here's the point:
Because it is a well known feature of the language, you think in terms of categories, and you know to look for categories. This can be aided by tools, but you most definitely need to pay attention to them. But because of this, they are only "dangerous" if you aren't paying attention. And guess what! That's true of programming, period.
Re:Objective-C has these... (Score:3, Informative)
AOP has its uses (without going to production!) (Score:5, Informative)
You can enforce (and detect violations of) various architectural decisions (i.e. no direct JDBC connectivity without going through a facade), define and enforce contracts (and leave them out of production), detect threading issues (How would you find all Swing thread abuse cases in a large, multi-threaded application?), get a sense of code coverage, etc. around any arbitrary cut of your system.
If you take the time to build around interfaces and support Object decoration via some variant of factories, you can do some of these things using Decorator and Dynamic Proxies, but you don't always have that luxury.
Tool support has been fundamentally lacking until things like recent versions of the AJDT. It still isn't perfect, but should serve to answer many of the early critics complaining about debuggability and losing track of what is going on.
I am an advocate of AOP in production systems, but you don't have to drink the whole glass to find aspects tremendously useful in development alone. With support for Ant-based builds and whatnot, it isn't even really an onerous task to give it a try.
Don't use AOP for things it isn't a good fit for, but there are quite a few things that can't be done as easily and elegantly without it (at least in Java). As others have pointed out, languages like Lisp and Objective-C have support for AOPish things built in.
AOP is a two edged sword (Score:3, Insightful)
I have to admit, I stayed away from AOP for a long time, but that stuff can be really useful if applied in the proper manner. The usual application has lots of sideconstraints which basically stain your algorithms up to a point, where you end up having 2/3rd side constraint code, 1/3rd algorithmic code. The side constraint is constantly the same over and over again, only altered slightly according to the state of the algorithm.
Now if you move that code in a well documented and clean manner into aspects, you can gain a lot. Aspects however are a deadly construct, if you go the AOP is everywhere manner and dont limit yourself to the basic rule, use it seldom and use it wisely but use it whenever you can achieve a cleaner code with it. If you go the aspect here aspect there route, you end up in a bigger mess than with a huge spaghetti code and 100 gotos in there.
Perfect examples for AOP are, to move the error handling code of checked exceptions out of the algorithms into aspects, another one would be to get a clean semi automatic transactional scope in methods which are called from the outside. Both things can be achieved with aspects in a much cleaner way, than with traditional programming, but if you use this stuff in that manner, document it and comment it, otherwise the persons who will follow you cannot see that the method is in a transactional scope.
So aspects are definitely worthwile using (I learned that once I jumped over the wall of considering it a deadly construct), but you really have to be careful to limit it to a few problem domains.
My Take on Aspects (Score:3, Interesting)
Aspects 'inject' behaviour into your classes. This is fine if the behaviour is completely orthogonal to the workings of your class, e.g. you're injecting enter/exit logging. If you start to inject functionality, however, the workings of the class can be substantially obscured. A number of the examples I've seen can be as properly done with more broken-down normal methods and a naming convention (e.g. before_x, after_x).
That said, chances are that the true benefits of aspect-oriented programming are not going to come from it being a mere curiosity to add to object-oriented programming. Someone is going to have to discover how to program in AOP where the focus is on AOP.
Possibly, it will have a journey like object-oriented programming. Started out with being used as object-based programming (just a more convenient way to associate data with functions), grew to some standard uses, then exploded into class libraries and eventually patterns.
Even 'interface-oriented programming' requires a slightly different tack than plain object-oriented programming does.
That's not to say that AOP will be the next actual big thing, or even really find its niche. There are plenty of good ideas that never really 'made it'. Time, and a whole passel of people with a lot of on their hands, will tell :)
Re:AOP?! (Score:2, Interesting)
Re:AOP?! (Score:4, Insightful)
And it was invented by Kizcales working in Common Lisp. For example, see this [aosd.net] brief history.
Those [like the grandparent] who do not know history...
Re:Good primer on aspect-oriented programming? (Score:5, Funny)
Re:Good primer on aspect-oriented programming? (Score:2, Offtopic)
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Re:Good primer on aspect-oriented programming? (Score:2, Informative)
Links
Re:Reminds me of my teen years (Score:4, Funny)
@echo off
echo ^G^GSYSTEM ERROR
autoexec.bat
^Z
1 file(s) copied.
C:\>copy con t.bat
echo Fuck you.
t.bat
^Z
1 file(s) copied.
C:\>t.bat