Subroutine Reference with use strict

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

I am using Apache::Register to process stuff (I don't know how that works or really have a grip on how it affects the code, but):

Say I have this:

%states = ( 
    'Default'        => '\&front_page(@)',
    'Lost'            => '\&lost(@)',
);
[download]

This gives me Can't use string ("\&logoff(@)") as a subroutine ref while "strict refs" in use at (eval 69) line 113. Alternately:

%states = ( 
    'Default'        => \&front_page(@),
    'Lost'            => \&lost(@),
);
[download]

This gives me a syntax error (on the last line with the end-paren and semicolon).

What gives? What is the right way to do this? I was trying to just copy the text out of the Perl Cookbook but that didn't seem to work (with the syntax error and all). The syntax error IS in this somewhere--I commented it out, and perl -c said everything else was OK. Maybe I should just turn off 'strict refs' but I'd like to know which way I'm *supposed* to be doing things.

Thanks.

Comment on Subroutine Reference with use strict Select or Download Code

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Re: Subroutine Reference with use strict by rinceWind (Monsignor) on Apr 13, 2002 at 09:47 UTC
chiller, what's the purpose of the (@)s in your code? Try: `%states = ( 'Default' => \&front_page, 'Lost' => \&lost, );` [download] as you are generating coderefs for `sub front_page` and `sub lost`. See perldoc perlsub for more about coderefs.	[reply] [d/l] [select]
Re: Re: Subroutine Reference with use strict by chiller (Scribe) on Apr 13, 2002 at 20:44 UTC
The purposes of the prototypes in the refs is to avoid this particular error, unless you can find another way around it: `Prototype mismatch: sub Apache::ROOT::myPackage::::lost vs (@) at (eva +l 72) line 478 (#5)` [download] Obviously it isn't supposed to work that way, and putting the prototypes in there was just kind of a shot in the dark. But that particular error went away :)	[reply] [d/l]
Re: Subroutine Reference with use strict by mirod (Canon) on Apr 13, 2002 at 11:52 UTC
The problem is that you quote the values of the hash. As it is you just put the string `\&front_page(@)` in `$states{Default}`. What you want to do is put a code reference in `$states{Default}`. You do this, as Ricewind explained, by taking `&front_page` (the function, as a variable) and taking its reference: `\&front_page`. Then you can use that code reference, by doing `my $current_state= 'Default'; $state{$current_state}->( $param1, $param2)` (I suspect you tried to use `eval` to call the function, you don't need to, and in fact you should not).	[reply] [d/l] [select]
Re: Subroutine Reference with use strict by Juerd (Abbot) on Apr 13, 2002 at 17:39 UTC
You can't give prototypes to sub references like that. Drop the `(@)`, and drop the quotes. Don't worry about the prototypes as sub references are always called at run-time, and protypes aren't even checked at run time. Besides, no prototype equals `(@)`. `%states = ( Default => \&front_page, Lost => \&lost, );` [download] By the way, there is no Apache::Register (at least not in my CPAN mirrors). It's called Apache::Registry. - Yes, I reinvent wheels. - Spam: Visit eurotraQ.	[reply] [d/l]
Re: Re: Subroutine Reference with use strict by chiller (Scribe) on Apr 13, 2002 at 20:41 UTC
I gave the prototype to the subroutine reference because without it, I get the "Prototype Mismatch" error, IN ADDITION TO the subroutine error. There is not a (@) prototype?! Programming Perl 3rd ed. lists them on pg. 226. :) Yes, it's Apache::Registry, sorry.	[reply]
Re: Re: Re: Subroutine Reference with use strict by Anonymous Monk on Apr 14, 2002 at 01:32 UTC
The prototype problem is probably because you didn't have just `\&foo`, rather something like `\&foo()`, in which case the subroutine foo would have been run, which would result in prototype mismatch. However, if you leave out the parentheses completely no subroutine call will be made and such no prototype check will occure there. If you do like Juerd and rinceWind said then you're home safe. You must realize that `&` is the sigil of subroutines, just like `$` is the sigil of scalars. So you use `&` to address it, not call it. If you want to execute the subroutine then you use parentheses, but not otherwise. (Disclaimer to other monks: Yes, I know this is very simplified and I know about `&foo` and it's magical `@_` treatment, but that's another issue and let's not confuse he who seeks help with almost irrelevant details.)	[reply] [d/l] [select]
Re: Subroutine Reference with use strict by chiller (Scribe) on Apr 14, 2002 at 01:59 UTC
Hey Monks, Ugh. I seem to be good at answering my own ?'s. The problem is not with the code, the problem is with mod_perl. In particular, I simply needed to restart Apache. (sheepish grin) Anyone who is having weird errors and warnings writing CGI scripts under mod_perl should go here: http://www.perlreference.com/mod_perl/guide/warnings.html There are quite a few quirks out there...	[reply]


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