Subject: Re: Declaring type of top-level (special) variables? From: Erik Naggum <erik@naggum.net> Date: Fri, 12 Apr 2002 22:20:27 GMT Newsgroups: comp.lang.lisp Message-ID: <3227638826875433@naggum.net> * Adam Warner | I guess this means by using DECLARE I could create programs with | unintended security holes (buffer overflows, etc.) No. Please hold your conclusions until you know what kinds of things are declared in Common Lisp. For your edification: Through all my years of Common Lisp study and use, approaching 15, now, I have never seen or heard of any security-related problems in Common Lisp systems that could be traced back to misdeclaring types, and you would have to go to such lengths to be able to overflow a buffer that it had to be done with full intent and premeditation, not by the kind of accident that produces security holes in languages that require serious effort to aim your high-powered machine gun away from your feet. | Certainly not the kind of functionality I was looking for (where I could | enforce a specific type on a variable). Well, this is not how Common Lisp declarations work in the first place. What do you want to happen? Should the compiler yell at you for not storing the appropriate type of object in a variable? That is simply not how Common Lisp systems work, either. For the time being, please ignore declarations completely. They have much more potential to confuse you than to illuminate you at this point. It might be instructive to regard every function as returning objects of type t and every caller as passing objects of type t, and to think about what this would do to your code. When you have thought about this for a while, you realize what it takes to implement a Common Lisp system in safe mode, and why it is a fantastic feature of the language that you can ex(ect the language substrate to catch all of your violations for you. You should therefore not even _try_ to request anything less than maximum safety until you have learned to write code that is equeally defensive yourself. If you include the following in all your source files, you should never have any problems: (declaim (optimize safety)) When you have learned to write safe code yourself and know how to ensure that your functions operate within a world of known types, you can start declaring your types and turning the safety down. If you find that you need better performance, you are jumping the gun. The Common Lisp way is to write correct code before you write fast code. If you spend only half as much time as you would getting fast C++ code correct on making correct Common Lisp code fast, you would get approximately equally good performance, so this is not the overall loss that it seems to be to someone who is used to writing fast and incomplete or incorrect code. /// -- In a fight against something, the fight has value, victory has none. In a fight for something, the fight is a loss, victory merely relief. Post with compassion: http://home.chello.no/~xyzzy/kitten.jpg