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Postings from February 2003
Nick XS and Porters,
I have painfully learned that binmode(FH => ":layer") STACKS layer
instead of overwriting the layer. In other words,
binmode(FH => ":first"); binmode(FH => ":second");
means
binmode(FH => ":first :second");
Nick, I think this is rather a feature instead of a bug but see this.
# Module.pm
package Encode::ROT13;
use base qw(Encode::Encoding);
__PACKAGE__->Define('rot13');
sub encode($$;$){
my ($obj, $str, $chk) = @_;
$str =~ tr/A-Za-z/N-ZA-Mn-za-m/;
$_[1] = '' if $chk; # this is what in-place edit means
return $str;
}
# Jr pna or ynml yvxr guvf;
*decode = \&encode;
package Module;
binmode STDOUT => ":encoding(rot13)";
1;
# main.pl
use Module;
# binmode STDOUT => ":encoding(rot13)"; # Comment me out and see!
print "Perl\n";
__END__
With binmode() in main.pl commented out, main.pl prints "Crey", just as
expected. But when you uncomment that, it magically prints "Perl" !
This counterintuitive nature of binmode() was accidentally found by
SUGAWARA Hajime <sugawara@hdt.co.jp> when he tried to 'use encoding
"euc-jp";' both in his module and script. Since encoding.pm implicitly
binmode()s STDIN and STDOUT, something totally unexpeded happened.
For the time being I have made a patch to encoding.pm so it inimport()s
before import()s (Actual patch right after the signature) to make it
behave as expected. But considering the facts:
* That filehandles are global -- what if the modules called installs
the layer and the user of the module has no idea that it does?
* There is no known way to tell what layers a given filehands are in --
so you can't sensibly binmode(FH => ":pop") ?
the behavior of binmode() should be modified so that it overwrites
instead of stacks.
Dan the Encode Maintainer
diff -u -r1.41 encoding.pm
--- encoding.pm 2003/02/06 01:52:11 1.41
+++ encoding.pm 2003/02/26 07:39:21
@@ -39,6 +39,7 @@
require Carp;
Carp::croak("Unknown encoding '$name'");
}
+ __PACKAGE__->unimport; # clean up binmode
$name = $enc->name; # canonize
unless ($arg{Filter}) {
$DEBUG and warn "_exception($name) = ", _exception($name);
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