However, in my example, the contents of the string passed to encode_utf8 were not code points - there were already in UTF8, and were therefore left unaltered by encode_utf8.
No. The string passed to encode_utf8 did contain codepoints; that's what Perl strings are. And the function returned something that was different from the original string, as can be seem below: 
use strict;
use warnings;

use Encode;
use charnames qw(greek);

for ("ABCD", "ABC\N{delta}", "\N{alpha}\N{beta}\N{gamma}\N{delta}") {
    printf "orig len=%d, enc len=%d\n",
    length($_),
    length(Encode::encode_utf8($_));
}
__END__
$ perl /tmp/p
orig len=4, enc len=4
orig len=4, enc len=5
orig len=4, enc len=8

[download]
How the string is internally represented in Perl is (almost always) completely irrelevant. Perl sees strings as a list of codepoints; typically if all the codepoints are < 256, perl stores them using one byte per codepoint; if any are >= 256, it stores them all as a variable number of bytes using (as it happens) utf8 encoding internally.

Regardless of a string's internal coding, Encode::encode_utf8() returns a string consisting of a codepoint for each the octets of what would be the utf8 representation of the original string, ragardless of how that original string was actually stored internally.

Dave.

In reply to Re^3: What does Encode::encode_utf8 do to UTF-8 data ? by dave_the_m
in thread What does Encode::encode_utf8 do to UTF-8 data ? by scollyer

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