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Re: What does a failed regular expression match actually return? (updated)by haukex (Archbishop) |
on May 20, 2020 at 09:36 UTC ( [id://11116971]=note: print w/replies, xml ) | Need Help?? |
Usually where Perl operators return false they do so by either returning an empty string or 0 Actually, they return both at the same time. What is the actual value returned by a failed regular expression match? Please see this table of regular expression return values. print Dumper( "a" =~ m/b/ ); is providing list context to its arguments, so it's the same as writing print Dumper( ); Why does ... !~ returns the more common empty string version? Because "a" !~ m/a/ is the same as !('a' =~ /a/), and that returns Perl's special false value. Update: Your initial issue can be solved by scalar or PerlX::Maybe:
Eventually I realised that the failed match for the regular expression was somehow tricking the first comma to be evaluated in a scalar context, rather than a list context (note that if the regular expression matches then it returns 1 and the comma is evaluated in a list context). Sorry, no, your analysis is not correct - the hash assignment is entirely in list context, in the examples you showed there's no scalar context going on there at all; only in the my $a = ... assignments. Update 2: To nitpick myself a little, the arguments to the =~ operator are in scalar context.
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