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Re: Declaring a Variable [for BEGINNERS]

by Old_Gray_Bear (Bishop)
on Dec 27, 2006 at 20:27 UTC ( #591933=note: print w/ replies, xml ) Need Help??


in reply to Declaring a Variable [for BEGINNERS]

That is one way to do it, but....

My personal preference is to 'declare' the variable in the scope where it will be used, rather than having a huge clump-o-names at the start of the code. There are at least two reasons for this:

  1. I don't like leaving variables exposed to the vagaries of later maintenance coders. (Coders, please note, as opposed to programmers.) There is a tendency for Coders to look for an 'unused' variable when they are making enhancements, and grabbing one from the clump at the front is just so tempting. ("Hey, I saved allocating another variable! I'm being Efficient and Reusing code and all that Best Practice Stuff....")
  2. A clump-o-variables is a strong indication of maintenance headaches to come. That variable you saved in (1), well you changed its value didn't you? And you didn't save the old value so you could restore it after you were done, did you? Your new Code Works, but you have introduced (potentially) bugs in the Old Code that depended on the value in that Global Variable that you just stomped on....
  3. A clump of declarations makes it harder to figure out where the logic starts, unless you are very very clear with your comments. How many times have I run across  my $var;$var=fps(1.234);$mumble=tilde($var);my next_vat; buried in the middle of a bunch of declarations?
  4. A Clump-O-Variables at the start of your code means you have a Clump-O-Global-Variables. Global variables have 'action at a distance' properties.
As for
use strict; # Note: all in lower case use warnings;
Don't start coding without it. (And don't start me on that rant again!)

The clump-o-variables (and it's sibling the clump-o-subroutines) is often the hallmark of someone who has written a lot of C or Shell, where you really had to declare before use. The Perl compiler is a little brighter than that. Constructing your code so that it assists in understanding the logic-flow is a good thing. Clumps of things that impede the understanding should be avoided.

That said, the clump-o-something is a valid way to write Code. It's not a style I like, or encourage. But it is a valid style, if it fits your way of seeing the Code. Just bear in mind, if I am the next programmer to do maintenance on this, I may drink an awful lot of coffee before I understand how my fix should fit in. (And a Wired Old Bear is not exactly a pretty sight...)

Update -- Fixed broken link; thanks (ysth).

----
I Go Back to Sleep, Now.

OGB


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Re^2: Declaring a Variable [for BEGINNERS]
by talexb (Canon) on Dec 28, 2006 at 09:55 UTC
      The clump-o-variables (and it's sibling the clump-o-subroutines) is often the hallmark of someone who has written a lot of C or Shell, where you really had to declare before use. The Perl compiler is a little brighter than that. Constructing your code so that it assists in understanding the logic-flow is a good thing. Clumps of things that impede the understanding should be avoided.

    If I can come to the defense of C, both languages permit you to declare locally scoped variables at the start of a block. Only in Perl can you declare variables mid-block, although I haven't tested that recently.

    Alex / talexb / Toronto

    "Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds

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