Thanks, that's right. Its because io() will emit an overloaded object so stringification would trigger.

You'll have to "peel off" the overloading, so to speak, by invoking overload::Overloaded (though funny, the perldoc says this should "true if 'arg' is subject to overloading...", wasn't expecting an actual GLOB object there.)

% perl -de 0 -MIO::All -MData::Printer

Loading DB routines from perl5db.pl version 1.51
Editor support available.

Enter h or 'h h' for help, or 'man perldebug' for more help.

main::(-e:1):    0
  DB<1> $io = io '.zshrc'

  DB<2> x overload::Overloaded( $io )
0  GLOB(0x17a4378)
   -> *IO::All::((
  DB<3> $o = overload::Overloaded( $io )

  DB<4> Data::Printer::p($o)
\ *IO::All::((  (layers: )

  DB<5>
[download]

It would probably make a nice exercise to implement a Data::Printer filter for this.