From @garfieldnate

I want to retrieve the mode that a handle was opened in via B, but the values of "append" and "read and write" are mutually exclusive, so information is lost if a handle is opened with both and then inspected via B. To demonstrate​:

use strict;
use warnings;
use B;
use File​::Temp;
my $temp_fh = File​::Temp->new();
$temp_fh->close();
my $filename = $temp_fh->filename;
foreach my $mode (qw( < > >> +< +> +>> )) {
  open(my $fh, $mode, $filename) || die "Can't open temp file in mode $mode​: $!";
  my $type = B​::svref_2object($fh)->IO->IoTYPE();
  print "$mode -- $type\n";
}

The above prints the below​:

< -- <

-- >

-- a
+< -- +
+> -- +
+>> -- a

These all make sense except for the last one, which should be "a+" or something.