A user on the DALnet #perl channel presented an interesting problem today. His CGI program was die'ing with the following exception: 

Can't locate object method "new" via package "IO::Handle" (perhaps you
+ forgot to load "IO::Handle"?) at <line number>;

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The indicated line number was the following attempt to invoke the class method &CGI::new: 

my $q = new CGI;

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I thought perhaps there was some ambiguity about the intent of the method invocation, so I suggested using 

my $q = new CGI::;

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to force perl to parse 'CGI' as a package name, but to no avail. After looking over the code for twenty minutes or so, I finally noticed that there were several open() statements that opened a filehandle named, you guessed it, 'CGI'. I guessed that CGI was being made an IO::Handle object at compile time, and that the subsquent attempt to invoke the &CGI::new class method was actually being interpreted as an IO::Handle instance method invocation against the non-existent method &IO::Handle::new.

As a test, I moved the invocation of the CGI:: constructor to a BEGIN block, and everything seemed to work as expected.

This demonstrates the problem: 

$ perl -MCGI -e 'my $q = new CGI::; open CGI, "~/foo.txt";'
Can't locate object method "new" via package "IO::Handle" (perhaps you
+ forgot to load "IO::Handle"?) at -e line 1.

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The obvious workaround is to refrain from using filehandles with the same names as packages, but this is the first time I've run into this problem. I tested this in perl versions 5.005_03, 5.6.0 and 5.6.1, by the way.

Is this breakage in perl, or have I missed a big fat "don't do this!" somewhere in the POD?

conv

In reply to Filehandles vs. Packages: And the winner is... by converter

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