AFAICT, the effect of pack('U0C*', unpack('U0C*', ...)) is the same as utf8::upgrade. See also What does utf8::upgrade actually do.

use warnings;
use strict;
use Devel::Peek;

my @tests = (
    "Hello",
    "Hell\xF6",
    "\N{U+20AC}",
    "\xE2\x82\xAC",
);

for my $in (@tests) {
    my $out = pack('U0C*', unpack('U0C*', $in));
    print STDERR "##### ##### ##### pack/unpack ##### ##### #####\n";
    Dump($in);
    Dump($out);
    print STDERR "##### upgrade #####\n";
    Dump($in);
    utf8::upgrade($in);
    Dump($in);
}
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This is what I suspected it was doing when I saw the question. I did not have a chance to verify it.

Seeking work! You can reach me at ikegami@adaelis.com

Yup, confirmed that changing to the "upgraded" internal storage format is the only effect other than making a copy.

Seeking work! You can reach me at ikegami@adaelis.com

G'day jjmoka,

Your assumption seems reasonable. Here's a test script:

#!/usr/bin/env perl

use strict;
use warnings;
use utf8;

use Test::More;

my @test_strings = qw{ abc абв αβγ 🌌🪐🚀  🏻🏼🏽 𓀀𓀁𓀂 ◌◌◌̂ };

plan tests => 0+@test_strings;

ok $_ eq pack('U0C*', unpack('U0C*', $_)) for @test_strings;

Output:

1..7
ok 1
ok 2
ok 3
ok 4
ok 5
ok 6
ok 7
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As you suggest, there may be special cases. I couldn't think of any off the top of my head; other monks may know of some. You can just add more strings to @test_strings to test them (without needing to change anything else in the test script).

You just said "I've found this code". Knowing something about the source and context of that code may provide scope for better answers.

Thank you. I did some testing myself (even though less elegant). I can fill the gap of context but unfortunately the information doesn't help. This is actually just code I've found. Git points me to a 7 years old commit when the repo was moved from svn to git. The real author is only guessable but anyhow all these people already went coding somewhere else. For who is left with it, there is always, at least, this monastery to act like a lighthouse in the darkness.

>perl -wle "print 'ok' if 2.3 != unpack 'd', pack 'd', 2.3;"
ok
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Just as a confirmation (changed != to == and swapped the quotes around for *nix command line):

$ perl -wle 'print "ok" if 2.3 == unpack "d", pack "d", 2.3;'
ok
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— Ken

Just as a confirmation (changed != to == ....

Yes, if nvsize <= doublesize (not that nvsize is ever less than doublesize) then the equality holds.
Otherwise the equality doesn't hold.

... and swapped the quotes around for *nix command line

That was actually unneeded. (No big deal ... just FYI.)
The rendition that I posted works fine on both Linux and windows.
Perl one-liners inside double-quotes generally aren't a problem on Linux unless there's a scalar variable in the code - and I deliberately crafted my one-liner without inclusion of a scalar variable in order to achieve that portability ;-)

Cheers,
Rob

Nice, thanks.