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Re: Use globals or pass around everything under the sun?
by maverick (Curate) on Dec 04, 2001 at 11:54 UTC
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My advice is always to avoid global vars whenever possible. They are most always bad (say "I have 30 global variables, is that too many?" in the chatterbox and what happens). Machines are fast. Ram is cheap. I'd rather add a few clock cycles to the execution time than add a few hours to the debugging time.
As for a technique to apply... Instead of having 30 separate variables floating around, stuff similar groups of variables into either a module (as previously described) or use a hash. I describe the technique for using a hash here. Basically this is a best of both worlds scenario...to pass ALL your vars to your module you only have to copy 1 scalar if you us a hash ref (your coworker's big problem), you don't have tons of globals, and you don't have to remember the exact sequence of the 30+ vars you passed in.
HTH
/\/\averick
perl -l -e "eval pack('h*','072796e6470272f2c5f2c5166756279636b672');"
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Re: Use globals or pass around everything under the sun?
by BMaximus (Chaplain) on Dec 04, 2001 at 11:55 UTC
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Ok, repeat after me ...
"Global variables are bad"
"Global variables are bad"
"Global variables are bad"
"Read Code Complete by Steve McConnell"
As you can see I try to avoid global variables at all cost. If the number of variables your are passing to modules/functions is over 10. You need to take a look at what you're doing again and rethink it. Try to combine variables that are related and pass them as a hash.
Look at CGI::Application as a large framework for web applications. If its a stand alone program you can still get an idea as to how you can organize things.
You're not too clear as to what you're doing. But in any application if you're passing too many variables in to give it information, you're more likely to have problems. Both in tracking down where it is and how many crop up as well as how much time it takes to create it. Try to break the task down as much as you can. You'll find you can reuse code in a lot of places and save a lot of time.
The more you reduce the load on the database, the better your application will run. Though having 30 or more variables going to a module won't slow the application down, it just makes it more complicated. Just remember you have to keep track of all those variables.
Work on getting the job done first, then optimise it for speed.
BMaximus | [reply] |
Re: Use globals or pass around everything under the sun?
by jepri (Parson) on Dec 04, 2001 at 11:08 UTC
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Re (tilly) 1: Use globals or pass around everything under the sun?
by tilly (Archbishop) on Dec 04, 2001 at 18:33 UTC
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My reaction to what you describe is that both of you need
to improve on design so that you don't think that you really
need 30 variables all of the time. I wish I had a simple
way to tell you how to do that, but without understanding
why you are getting into that bind, I cannot really tell
you how to avoid needing that many variables. (I suspect
that understanding that phrase, Think loose coupling
that you see from time to time on pages here might help.)
But after that, both solutions have problems. Globals raise
the possibility of promiscuous interaction between code,
which causes all of the usual debugging issues. Passing
variables protects you from that, and documents what you
are using, but raises issues with how your argument lists
are structured. If you are positionally placing 30
arguments, then you are using copy and paste. What happens
if you want to add an argument? Hopefully you are using
hashes to allow you to work by name.
Likewise the answers that people are offering have issues.
If you start using hashes, how do you do typo checks? I
have offered solutions to that in the past.
But most of those solutions (rightly IMO) require you to
wind up carefully thinking through which variables are
needed in which functions. Passing references to hashes
you directly access is likewise problematical for the
reasons that I stated at Pass by reference vs globals.
No. The real problem is that you are trying to manage a
large amount of common data. That is a task which raises
inherent issues. And solving that is probably a design
issue. | [reply] |
Re: Use globals or pass around everything under the sun?
by dragonchild (Archbishop) on Dec 04, 2001 at 18:32 UTC
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Use hashes or, even better, hashes-that-can-have-methods-called-through-them (aka, objects). This will allow you to bundle stuff.
(You will be using references to hashes, not the hashes themselves, right?)
You are correct in that passing in tons of variables will make the code cleaner. You have an interface between the main program and the modules.
As for the other programmer's thoughts, he's probably right. But, he also suffers from premature optimization. Is passing the variables around causing a noticeable slowdown? If it isn't, then there's nothing to optimize!
My suggestion would be to try them both.
What's that you say? Too much work? Your implementation is too tightly tied to your interface? Sounds like you've got work ahead of you. :-)
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We are the carpenters and bricklayers of the Information Age. Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement. | [reply] |
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Im so glad you posted this. Its basically what I was going to say too.
Whenever I find I am dealing with large numbers of parameters getting passed around I create an object to hold them all, and then either pass it around or subclass it.
One advantage to having an object to pass around is that it provides an single point that the programmer can go to see what possible variables exist. This is in some respects better than subclassing as you dont have zillions of layers of additional stuff.
My only criticism of you post is that IMO there should not be more than a few parameters to a suboutine. The more parameters a subroutine takes the more difficult it is to understand what it does, and to make mistakes with regard to their position (addmittadly this can be dealt with via named parameters) or omission. Usually this isnt that big a deal, except that it can have a dramatic slowdown on development time and frustration levels.
Yves / DeMerphq
--
Have you registered your Name Space?
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Heh. I wasn't going to get into refactoring, though that sounds like what's needed here...
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We are the carpenters and bricklayers of the Information Age. Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.
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Re: Use globals or pass around everything under the sun?
by lachoy (Parson) on Dec 04, 2001 at 12:59 UTC
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While I didn't comment in that thread, my sympathies went
with jbert at Re: how to make a universally inherited method?. In particular I fail to see
what using singletons in this case really buys you over
using strict.pm and exporting variables from a
configuration module using Exporter. (Other than
buzzword compliance that is.)
There are valid uses of a Singleton pattern where it is a
win. If producing your variable is expensive, and so you
want to do it lazily, then Singletons are great. They are
then basically an OO way of expressing memoization. But
for just expressing configurations, what is the big win
supposed to be?
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It's probably just me, but I find exporting variables for configuration purposes just as bad as a global variable. I hate polluting namespaces except for CONSTANTS, even when the coder asks for it, and always fully qualify all non-method subroutine calls. Paranoid? Maybe, but I think it's made my code easier to understand down the road.
As you said, it's basically the same thing as exporting a variable but with an extremely lightweight wrapper around it that explicitly tells you (the maintainer twelve months down the road after the original programmer has left) there's only one configuration object out there. TMTOWTDI.
Chris
M-x auto-bs-mode
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When I supported the use of singletons in that thread, it was to say that anything is better than a bunch of globals. What I was proposing was exporting wrapper functions using Exporter. I also don't know the definition of a singleton, so I was guessing from context. I think I guessed wrong. :-)
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We are the carpenters and bricklayers of the Information Age. Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.
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Re: Use globals or pass around everything under the sun?
by greywolf (Priest) on Dec 05, 2001 at 21:37 UTC
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Thanx for the replies and the info everyone.
You have given me some good ideas to think about. While I am not the head designer of this project I will be sure use as much as I can.
mr greywolf | [reply] |
