Re: "when" and replacements

The given ... when construct does a smart match ~~ on the expression after the when EXCEPT in the following cases:

a subroutine or method call
a regular expression match, i.e. /REGEX/ or $foo =~ /REGEX/ , or a negated regular expression match (!/REGEX/ or $foo !~ /REGEX/ ).
a comparison such as $_ < 10 or $x eq "abc" (or of course $_ ~~ $c )
defined(...), exists(...), or eof(...)
a negated expression !(...) or not (...) , or a logical exclusive-or (...) xor (...)
a filetest operator, with the exception of -s , -M , -A , and -C , that return numerical values, not boolean ones.
the .. and ... flip-flop operators.

Regex-replacements are not in that list, but a negated expression is, therefore your !! trick worked.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

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Re^2: "when" and replacements by John M. Dlugosz (Monsignor) on May 07, 2011 at 07:08 UTC
I'm postulating that it ought to be added to that list. It "feels like" the plain match, and adding the =~ directly "feels like" the `$_<10` case.	[reply] [d/l]
Re^3: "when" and replacements by CountZero (Bishop) on May 07, 2011 at 07:21 UTC
To be true, I also had some trouble before I got my head around this `given ... when`. The whole idea of the default smart match takes some time to getting used to. If I want a smart match, I'll ask for one, explicitly, in all other cases I use something else, explicitly. CountZero A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James	[reply] [d/l]
Re^4: "when" and replacements by John M. Dlugosz (Monsignor) on May 07, 2011 at 08:53 UTC
using `$_ =~` at the beginning of the stuff in parens should be enough to indicate "I don't want a smart match"; evaluate it the same as a mundane `if` statement, in the same way as the relational operators. After all, I might want the single-branch feature of `when` and have other cases that do use more usual match criteria.	[reply] [d/l] [select]
Re^4: "when" and replacements by LanX (Saint) on May 07, 2011 at 09:01 UTC
Yeah, thats the reason why I never use `give/when` and prefer the `for/if/elsif/last` workaround. Cheers Rolf	[reply] [d/l] [select]