Re: :encoding() layer modifies read-only scalars

* Nick Ing-Simmons wrote:
>>>  Enocde 2.08, PerlIO::scalar 0.02, ActivePerl 5.8.2, 
>>>
>>>  #!perl -w
>>>  use strict;
>>>  use warnings;
>>>  use Encode;
>>>  
>>>  my $string = encode(UTF16 => "");
>>>  
>>>  for (qw/UTF-8 UTF-16LE UTF-16BE UTF-32LE UTF-32BE/)
>>>  {
>>>    my $backup = $string;
>>>    open F, "<:encoding($_)", \$backup;
>>>    my $char;
>>>    read F, $char, 1, 0;
>>>    close F;
>>>  
>>>    die unless $backup eq $string;
>>>  }
>
>There are no "readonly scalars" there.

It is opened for input according to `perldoc -f open` which suggests
that it should not be written to it. I would neither expect that the
code above modifies the scalar if it was opened for input and output
though, as I do not ask for any write operation. At least I am not
aware of documentation from which I should expect the behavior.

>Personally, I would be more motivated to fix whichever is at fault 
>if you explain why you are trying to read one character from 
>a stream with no characters in it (except a BOM).

I think I ran into this while looking for better Encode usage for my
HTML/XHTML/XML document encoding detection module HTML::Encoding which
needs to do some trial and error decoding; for example, the module
attempts to check the document for a byte order mark and currently does
so by encoding U+FEFF in suspected encodings and compares the resulting
octets with the octets of the document. Reading the first character from
the string and comparing it to U+FEFF might make more sense than that, I
thus looked into doing that and ran into this unexpected behavior.
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