in reply to Re: Re: Re: Simplifying code (Not obfuscation)
in thread Simplifying code (Not obfuscation)

Again, a very welcome and highly appreciated post, highlighting to me the existance of and difference between "if" and "or".

I won't pretend to understand the meaning of precedence in this context but I don't think that stops me understanding the pertinent points of your post.

That said, looking closely at the if solution I would have thought that would die if the system call actually succeeded. Am I missing something?
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Re: Re: Re: Re: Re: Simplifying code (Not obfuscation)
by Molt (Chaplain) on Mar 04, 2003 at 13:56 UTC

    No, you're quite right. I was being stupid and messed up, will correct that in a second so as not to confuse others.

    The precedence issue is moderately easy to explain in this context. There's a standard Perl idiom

    open FILE, "file.txt" or die "Error: $!\n".

    This is the equivilent to

    open (FILE, "file.txt) or die "Error: $!\n"

    as the 'or' is evaluated after the open command.

    If you were to try

    open FILE, "file.txt" || die "Error: $!\n"

    you may be surprised to know you'll never get the error message, this is because the || operator is evaluated before the open and so this is actually equivilent to

    open FILE, ("file.txt" || die "Error: $!\n")

    and so would only die if the string literal "file.txt" was blank. Not good. You get a similar thing with thing happening quite often.

    Moral of this story: Generally use || for defaulting values ($a = $b || $c), but use 'or' for logic control similar to the above.

    Oh yeah, and make sure your code dies when it gets an error, not when it doesn't.. I seem to have failed on this one

      Thanks for taking the time to explain that and for doing it so well.

      My future coding should be much improved because I can now consider such issues as this and how to test for errors. At the moment it's all a mish mash of other people's code, cut and pasted. It will be good to be able to write these things from scratch myself.

      I have copied your post into my 'reference' notes. So I shouldn't ever need to ask the question again.