Question

What could here be wrong: I get the error-message
new: Unicode string must be given at ...
for the line
$gvalue = Unicode::GCString->new( $value );

use Unicode::GCString;

# ....
# ....

my $width = 0;
my $gvalue;

if ( $value ) {
    $gvalue = Unicode::GCString->new( $value );
    $width = $gvalue->columns();
}

# ....
# new: Unicode string must be given. at ...

---

$values comes form:

for my $i ( 0 .. $#$ref ) {
    for my $j ( 0 .. $#{$ref->[$i]} ) {
        my $value = $ref->[$i][$j] // '';
        # ...

Until now while testing $ref is hardcoded in script but then it should become a module and $ref should be shifted in a routine.

Answer 1

Unicode::GCString suffers from the Unicode Bug (assigns meaning to the UTF8 flag):

 $ perl -MUnicode::GCString -E'
    $_=chr(0xE9);
    utf8::downgrade($_);
    Unicode::GCString->new($_);
    say "ok";
 '
 new: Unicode string must be given. at -e line 4.

 $ perl -MUnicode::GCString -E'
    $_=chr(0xE9);
    utf8::upgrade($_);
    Unicode::GCString->new($_);
    say "ok";
 '
 ok

It expects a string in stored using the UTF8=1 internal storage format. You can force the string to the right format using utf8::upgrade, but it could also be a sign that you forgot to decode the string.