Re: Re: Re: 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?

Comment on Re: Re: Re: Image::Magick resize question Select or Download Code

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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.	[reply] [d/l] [select]
Re: or vs precedence issue by emilford (Friar) on Jun 09, 2002 at 15:31 UTC
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.	[reply]
Re^2: or vs precedence issue by Aristotle (Chancellor) on Jun 09, 2002 at 20:03 UTC
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.	[reply]


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