It's a bit strange, but the internal representation of the string shouldn't* matter.

What I do find very strange is that it doesn't croak when passed non-bytes. 

use strict;
use warnings;

use Data::Dumper qw( Dumper );

$Data::Dumper::Useqq  = 1;
$Data::Dumper::Terse  = 1;
$Data::Dumper::Indent = 0;

my $s = chr(0xC9);
utf8::downgrade($s);
print(Dumper(pack('V/a*', $s)), "\n");
utf8::upgrade($s);
print(Dumper(pack('V/a*', $s)), "\n");

print(Dumper(pack('V/a*', "\x{C9}\x{2660}")), "\n");

[download]

5.10.0: 

"\1\0\0\0\311"             # Ok
"\1\0\0\0\x{c9}"           # Ok
"\2\0\0\0\x{c9}\x{2660}"   # Does this make sense???

[download]

On the other hand, 5.8.8 was very broken: 

"\1\0\0\0\311"             # Ok
"\1\0\0\0\303"             # XXX
"\2\0\0\0\303\242"         # XXX

[download]
* — I realize it matters all to often, but that's getting fixed. In plfaces where it does matter, you can use utf8::upgrade and utf8::downgrade to control the internal format.

In reply to Re^2: Understanding pack and unpack changes for binary data between 5.8 and 5.10 by ikegami
in thread Understanding pack and unpack changes for binary data between 5.8 and 5.10 by dkg

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