Re: What is true and false in Perl?

"0 but true" is (a bit) interesting:

use strict;
use warnings;

print "0 but true"  ? "true\n" : "false\n";
print "0 but true" + 0 ? "true\n" : "false\n";
print "0 but true" + 1 ? "true\n" : "false\n";
[download]

No warnings using numeric addition on a string, despite the 'use warnings'. Also the second case is unexpected. Shouldn't 'True' + 1 be true?

Comment on Re: What is true and false in Perl? Download Code

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Re^2: What is true and false in Perl? by ig (Vicar) on Apr 17, 2009 at 02:32 UTC
More on this and other aspects of truth and falsehood are at Re: True or False? A Quick Reference Guide and http://stackoverflow.com/questions/129945/what-does-0-but-true-mean-in-perl.	[reply]
Re^2: What is true and false in Perl? by morgon (Priest) on Apr 17, 2009 at 01:06 UTC
Why is the second case unexpected? "0 but true" is not "True". It means "treat me in numeric context as 0, but in boolean context as true". So when you do "0 but true" + 0 you are in numeric context, so you effectively do 0+0 which is 0 and this in turn (for the ? operator) is false. I find that quite logical (which probably shows that using Perl for too long causes brain-damage). And by the way: You are not doing numeric addition on a string, you are evaluating "0 but true" in numeric context (to 0) - therefore no warning.	[reply]
Re^3: What is true and false in Perl? by ikegami (Patriarch) on Sep 15, 2009 at 17:53 UTC
And by the way: You are not doing numeric addition on a string, you are evaluating "0 but true" in numeric context (to 0) - therefore no warning. That makes no sense. The correct answer is that "0 but true" is special-cased. `$ perl -wle'print 0+"0 abc"' Argument "0 abc" isn't numeric in addition (+) at -e line 1. 0 $ perl -wle'print 0+"0 but true"' 0` [download]	[reply] [d/l]
Re^4: What is true and false in Perl? by Anonymous Monk on Apr 15, 2012 at 02:16 UTC
Only in the context of perl -e, as when run from a script, generates the same error (Argument "0 but true" isn't a numeric in addition (+) at line #. Also, both still print 0. And in both cases the attempt to add the string to 0 is ignored.	[reply]
Re^5: What is true and false in Perl? by AnomalousMonk (Archbishop) on Apr 15, 2012 at 02:42 UTC


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