?: conditional operators appear to fail

landau351 has asked for the wisdom of the Perl Monks concerning the following question:

The snippet below always fails when i test using the ?: operators but not when a full if() test is performed.
Why ??

-cheers landau351

#
# /usr/local/lib/perl5/5.6.1/sun4-solaris
#
$msgFile = "./data/err-PHY-opt.dat";
($msgFile =~ /\-opt.dat$/) ? $optsFile = 1 : $optsFile = 0;
print "optsFile = " . $optsFile . "\n";

if ($msgFile =~ /\-opt.dat$/)
{
    $optsFile = 1;
}
else
{
    $optsFile = 0;
} 
print "optsFile = " . $optsFile . "\n";
[download]

_{janitored by ybiC: Balanced <code> tags around codeblock, as per Monastery convention}

Comment on ?: conditional operators appear to fail Download Code

Replies are listed 'Best First'.
Re: ?: conditional operators appear to fail by Zaxo (Archbishop) on Aug 24, 2004 at 04:18 UTC
We've seen a similar question earlier today. Write it like this: `$optsFile = ($msgFile =~ /\-opt.dat$/) ? 1 : 0;` Trinary op returns a value, as `if () {} else {}` does not. It is the embedded assignments that goof things up for you. After Compline, Zaxo	[reply] [d/l]
Re^2: ?: conditional operators appear to fail by landau351 (Initiate) on Aug 24, 2004 at 04:33 UTC
thanx, i only just found the comments about the perlop precidence issue, i shall re-write. my code thanks again	[reply]
Re: ?: conditional operators appear to fail by tachyon (Chancellor) on Aug 24, 2004 at 05:38 UTC
In addition to Zaxos correct idiom it is useful to note you can use do{} in a ternary op which lets you say do: `$condition ? do{ $a = $b } : do { $c = $d }; $condition ? do_stuff() : do{ $stuff = NOT_DONE };` [download] ie mix assignments to different vars, assignment and function call etc. This is mostly useful if you are using it as a shortform idiom for if/elseif..... If you are just assigning different values to a variable based on some condition Zaxos `$var = $cond ? $val1 : $val2;` is the way to go. cheers tachyon	[reply] [d/l] [select]
Re: ?: conditional operators appear to fail by bart (Canon) on Aug 24, 2004 at 09:25 UTC
I don't see why you're not using `$optsFile = ($msgFile =~ /\-opt.dat$/) ? 1 : 0;` [download] which is how `?:` was intended to be used.	[reply] [d/l]
Re: ?: conditional operators appear to fail by Fletch (Bishop) on Aug 24, 2004 at 15:34 UTC
Also note that when you get strange behavior like this B::Deparse can help clear up how perl is parsing your code. `$ perl -MO=Deparse,-p -e '($msgFile =~ /\-opt.dat$/) ? $optsFile = 1 : + $optsFile = 0;' ((($msgFile =~ /\-opt.dat$/) ? ($optsFile = 1) : $optsFile) = 0);` [download]	[reply] [d/l]
Re: ?: conditional operators appear to fail by shenme (Priest) on Aug 24, 2004 at 20:59 UTC
Parenthesizing the truth value used with ?: is a good idea - usually. Got myself into a pickle the other day, though. `warn ($msg =~ m/\n$/) ? $msg : ($msg . "\n");` [download] didn't work quite as expected. After a bit'o head scratching about no results and complaints about "void context", I remembered the nastiness pointed out about 'print' and others, and realized the left paren was confusing the parser into thinking "warn()". In _this_ case, removing the parens worked better... `warn $msg =~ m/\n$/ ? $msg : ($msg . "\n");` [download]	[reply] [d/l] [select]