What an XS module does when it wants to process a list of bytes is of course up to the XS module's author

Ok - but I guess the module author (me) should probably document the procedure that the module takes. (The lack of any such documentation seems to have been a part of ribasushi's objection, and I think that's fair enough.)

For simplicity, let's stick to a single-byte string:

use Math::GMPz qw(:mpz);
my $z = Math::GMPz->new();
my $v = 255;
$str = chr(ord $v);
Rmpz_import($z, 1, 1, 1, 0, 0, $str);
print $z; # prints the value assigned to $v (ie 255).
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But let's say the user instead does a utf8::upgrade of the string, as per the following:

use Math::GMPz qw(:mpz);
my $z = Math::GMPz->new();
my $v = 255;
$str = chr($v);
utf8::upgrade($str);
Rmpz_import($z, 1, 1, 1, 0, 0, $str);
print $z; # now prints 195.
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The crux of the issue is "what do I (the module author) conclude regarding the expectation of the user that wrote that second block of code ? "

As I see it, I have only 3 choices:
a) conclude that the user's expected result is to see an output of "255";
b) conclude that the user's expected result is to see an output of "195";
c) conclude that I have insufficient information to know what output the user expects (except that the user will be expecting either "255" or "195").

Which is the correct conclusion for me to reach ?
I can accommodate either 'a)', 'b)', or 'c)' and I think the answer is probably 'c)', but I'd just like an informed opinion on that.

Cheers,
Rob

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