The arrow invocation produces the same result in this case:

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

conv

package Snafu;
use Carp 'cluck';
sub new {
   warn join ',',@_;
}
1;
Snafu::new("Test");
Snafu->new("Test");
[download]

package Snafu;
use Carp 'cluck';
sub new {
    cluck join ',',@_;
}
sub _new { goto &new }
1;
Snafu::new("Test");
Snafu->new("Test");
Snafu->_new("test");
[download]

perl -MCGI -e 'my $q = CGI->new(); open CGI, "~/foo.txt";'
Can't locate object method "new" via package "IO::Handle" at -e line 1
+.
[download]

-Blake

Even the least ambiguous object invocation fails here: perl -e "use CGI; $q= CGI::->new(); open CGI,'<cgi'" with the same error.

As far as I'm concerned, the first lesson here is Don't give your modules all-uppercase names, especially short ones. One of the changes for CGI is that it should be renamed Net::CGI.

I'm sick of not knowing whether someone is talking about C.G.I. or CGI.pm, CPAN.org or CPAN.pm, etc. B.pm and O.pm are just plain horrid names. And so on.

But, until that mess gets cleaned up (I won't hold my breath), realize that bareword file handles have been a problem forever and this is just one more reason to avoid them.

A third lesson is that all-uppercase tokens are now pretty heavily used by Perl and so you should always use mixed case in things you declare yourself that don't require a line-noise designator. That is, variable names are not a problem but function names and anything barewordish should be in mixed case these days.

        - tye (but my friends call me "Tye")

Oops, not what I was thinking at all!

Here are shorter example demonstrating the bug in more detail:

perl -e 'sub new{print@_} main->new(); open main, "foo";'
perl -e 'sub new{print@_} main->main::new(); open main,"foo";'
[download]

And the message from the second one gives a pretty solid indication what is going wrong. (I think that this is perlbug material.)

UPDATE
Since tye complained, the outputs respectively are:

Can't locate object method "new" via package "IO::Handle" at -e line 1
+.
GLOB(0x80d4208)
[download]