in reply to Re: Re: Image::Magick resize question
in thread Image::Magick resize question

Just a question on the notation used for the return value for Image::Magick::Read. I understand from merlyn's post that the Read function does not return a result in the error variable ($!).

Let's just pretend that it did return a value (even though it doesn't). Even then, wouldn't the line

$image->Read(file=>\*IMAGE) || die "Unable to read image: $!";

be better written as

$image->Read(file=>\*IMAGE) or die "Unable to read image: $!";

The difference being using or instead of ||. Not that it will do anything in this case, but when checking for return values in $!, is one not always suppose to use the "or" operator rather than "||"? I believe I was once told that using "or" (since it has a higher precedence) is always preferred when dealing with this type of situation. Did I hear wrong or am I right? Or does it depend upon the type of function called?

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or vs || precedence issue
by Aristotle (Chancellor) on Jun 08, 2002 at 22:51 UTC
    my $y = int rand 10 or die; This will work correctly since or binds losely. 10 is regarded as a parameter to rand which is regarded as a parameter to int; the result will be tested with or and die 1 out of 10 times. my $y = int rand 10 || die; This will never die since || binds tightly and causes 10 || die to be evaluated first. The result of that expression is then passed to rand as a parameter, and so on.

    Sometimes, very rarely, you actually want the tight binding rather than the lose, however.

    Makeshifts last the longest.

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      Cool! I was quite unaware of the difference between || and or. If it makes that much of a difference, I'll start using or in place of || when checking return errors. Thanks for the reply, the information was very useful.
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        Nononono. Not everywhere. Everywhere it belongs. Neither one is "the right one". Please take the time to understand exactly why they each work the way they do.

        Here's a hint: everything you can do with the one, you can also do with the other, as long as parens regulate precedence.

        Makeshifts last the longest.

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