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Prototype mismatch error - ChangeNotify

by merrymonk (Friar)
on May 20, 2011 at 13:11 UTC ( #905915=perlquestion: print w/ replies, xml ) Need Help??
merrymonk has asked for the wisdom of the Perl Monks concerning the following question:

I have got an error message that I do not know how to remove.
I would Google for it but since I do not understand what is wrong, this is proving difficult.
To confuse matters, the Perl seems work OK.
The error message is
Prototype mismatch: sub main::INFINITE: none vs () at …….lib/Exporter.pm line 64.
at …./Perl file.pl line 22 The Perl at line 22 is
use Win32::ChangeNotify;
The only line that uses ChangeNotify is
$notify = Win32::ChangeNotify->new($watched_dir, 0, FILE_NOTIFY_CHANGE +_SIZE);
How can I remove this error?

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Re: Prototype mismatch error - ChangeNotify
by John M. Dlugosz (Monsignor) on May 20, 2011 at 13:20 UTC
    The "prototype" is a declaration that a function will take arguments of a certain form. I think the error is saying that there are two conflicting declarations for INFINITE, normal and prototyped to take no arguments.

    I suspect that INFINITE is a constant created via use constant, and might be declared differently in different modules. (I see it is an "XS constant" in Win32::ChangeNotify) That is, Win32::ChangeNotify might declare it one way and some other module declare it another way.

    Move the Win32::ChangeNotify line higher up, so it happens first. Then the error will tell you the other place.

    That will tell you exactly what the problem is. If that guess is right, you can find exports of INFINITE in two different .pm files.

    Then you can post the details and module names and ask again for suggestions on remedying it. Perhaps one of the modules has it wrong and needs to be fixed. The modules in question might have a way to prevent the export. Or there may be general-purpose tricks to get around it but I don't know them off hand.

    I notice from the source that ChangeNotify is exporting constants by default, without mentioning that in the documentation nor providing a way to prevent it. Using () after the use line will prevent the import function from being called, but I don't know if that will prevent it from doing other things that are necessary, too!

    If the other place that imports it doesn't have a way to prevent it too, then a work-around would be to use it inside a dummy package. It is only used in one line, so delegate that line to a function in that inner package, which you call from the main code.

    You should complain to the module author for having default exports.

    —John

      By carrying out your suggested test, I identified the two modules as process.pm and changenotify.pm.
      I looked in both modules and could see both had INFINITE in the EXPORT. However, I could not recognize where either defined what INFINITE meant.
      Therefore I suspect that there is some incompatibility between these two.
      You also said “If the other place that imports it doesn't have a way to prevent it too, then a work-around
      would be to use it inside a dummy package. It is only used in one line, so delegate that line to a function in that inner package, which you call from the main code.”
      Although I have just Perl for some years it would help if you could give some more details.
      I guess I should know(!) but I simply do not understand what you mean particularly with the ‘so delegate’ part of it.
        I have had a very helpful reply from Christopher J. Madsen via RT bug-Win32-IPC@rt.cpan.org who suggested that in my case I can remove the problem by using
        use Win32::ChangeNotify qw(FILE_NOTIFY_CHANGE_SIZE);
        As this will just export _NOTIFY_CHANGE_SIZE from the module. Therefore there will not be any conflict with INFINITE. This worked so I no longer have a problem!
        Thanks for your help in pointing me in the right direction
        # this is the main file $x= Helper::foo(); # ... package Helper; use PoisonModule qw/ bar INFINITE/; sub foo { return bar (blah, blah, INFINITE); }
Re: Prototype mismatch error - ChangeNotify
by sierpinski (Hermit) on May 20, 2011 at 13:35 UTC
    Taken from CPAN:

    Constructor for a new ChangeNotification object. $path is the directory to monitor. If $subtree is true, then all directories under $path will be monitored. $filter indicates what events should trigger a notification. It should be a string containing any of the following flags (separated by whitespace and/or |).

    Something tells me that an underscore isn't the same as 'whitespace and/or |'. Give that a try and see if it works.

      FILE_NOTIFY_CHANGE_SIZE is not several options separated by underscores. It is one word, and is a constant exported from that module.

      If his line doesn't match the correct function call, that will be a problem for later. The compilation isn't getting that far, choking on the use.

      But the next paragraph does say “($filter can also be an integer composed from the FILE_NOTIFY_CHANGE_* constants.)” so that's the form he's using.

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