I didn't attempt to cater for your test ii because it was not part of the original specs.

Hmm, my apologies, I seem to be a bit myopic tonight. I didnt notice that comment. So tadmans solution pases under the rule change.

Still under my test scenario (the 'ii' case removed) all of your solutions generate warnings and fail. Sorry.

use warnings;
use strict;
use Carp;
local $SIG{__WARN__}=sub {die("\t@{[(caller(1))[3]]}() generated warni
+ngs!\n")};

my $foo = {
     aa => { O => 'zz',  C => 'yy'  }, #
     bb => { O => 'xx',  C => 'xx'  },
     cc => { O => undef, C => 'ww'  }, #
     dd => { O => 'vv',  C => undef }, #
     ee => { O => undef, C => undef },
     ff => {             C => undef },
     gg => { O => 0,     C => 0     },
     hh => { O => undef, C => 0     }, #
     #ii => { O => undef             }, # commented out because of rul
+es .
     jj => { O => 0,     C => ' '   }, #
     kk => { O => ' ',   C => 0     }, #
     ll => { O => undef, C => ' '   }, #
     mm => { O => ' ',   C => undef }, #
};

sub BUK{local($^W,$a)=(0,pop);grep{!exists$a->{$_}{O}or$a->{$_}{O}ne$a
+->{$_}{C}}keys%$a}
sub snw{no warnings qw(uninitialized);my$h=pop;grep{$h->{$_}{O}ne$h->{
+$_}{C}}keys %$h}
sub sg_{my$h=pop;grep{!(defined($h->{$_}{O}&&$h->{$_}{C})&&$h->{$_}{O}
+eq$h->{$_}{C}||!defined($h->{$_}{O}||$h->{$_}{C}))}%$h}
sub eg_{my$h=pop;grep{!(($h->{$_}{O}||$;)eq($h->{$_}{C}||$;))}%$h}
sub ddf{$a=pop;grep{$b=$$a{$_};defined$$b{O}!=defined$$b{C}||defined$$
+b{O}&&$$b{O}ne$$b{C}}keys%$a}#98
sub dex{$a=pop;grep{$b=$$a{$_};exists$$b{O}!=exists$$b{C}||defined$$b{
+O}!=defined$$b{C}||defined$$b{O}&&$$b{O}ne$$b{C}}keys%$a}#126
sub tad{my($h)=@_;grep{!exists($h->{$_}->{O})||(defined($h->{$_}->{O})
+?(defined($h->{$_}->{C})?($h->{$_}->{O}ne$h->{$_}->{C}):1):defined($h
+->{$_}->{C}))}keys%$h}#162
sub ukg{local$^W=0;my$a=pop;grep{!exists$a->{$_}{O}or$a->{$_}{O}ne$a->
+{$_}{C}}keys%$a} #85
sub ukf{local($^W,$a)=(0,pop);grep{!exists$a->{$_}{O}or$a->{$_}{O}ne$a
+->{$_}{C}}keys%$a} #87
sub ukh{$^W=0;$a=pop;grep{!exists$a->{$_}{O}or$a->{$_}{O}ne$a->{$_}{C}
+}keys%$a}

print "      Required: aa cc dd ff hh jj kk ll mm\n";
print "------------------------------------------\n";
eval { print "   tadman golf: @{[sort {$a cmp $b} tad($foo)]}\n"; };
print $@ if $@;

eval { print "BrowserUK golf: @{[sort {$a cmp $b} BUK($foo)]}\n"; };
print $@ if $@;

eval { print "sauoq No warns: @{[sort {$a cmp $b} snw($foo)]}\n"; };
print $@ if $@;

eval { print "    Sauoq golf: @{[sort {$a cmp $b} sg_($foo)]}\n"; };
print $@ if $@;

eval { print "  Elusion golf: @{[sort {$a cmp $b} eg_($foo)]}\n"; };
print $@ if $@;

eval { print " Demerphq defd: @{[sort {$a cmp $b} ddf($foo)]}\n"; };
print $@ if $@;

eval { print "Demerphq exist: @{[sort {$a cmp $b} dex($foo)]}\n"; };
print $@ if $@;

eval { print " browserUk f(): @{[sort {$a cmp $b} ukf($foo)]}\n"; };
print $@ if $@;

eval { print " browserUk g(): @{[sort {$a cmp $b} ukg($foo)]}\n"; };
print $@ if $@;

eval { print " browserUk h(): @{[sort {$a cmp $b} ukh($foo)]}\n"; };
print $@ if $@;

__END__
      Required: aa cc dd ff hh jj kk ll mm
---------------------------------------------
   tadman golf: aa cc dd ff hh jj kk ll mm
    main::BUK() generated warnings!
sauoq No warns: aa cc dd hh jj kk ll mm
    Sauoq golf: aa cc dd hh jj kk ll mm
  Elusion golf: aa cc dd jj kk ll mm
 Demerphq defd: aa cc dd hh jj kk ll mm
Demerphq exist: aa cc dd ff hh jj kk ll mm
    main::ukf() generated warnings!
    main::ukg() generated warnings!
    main::ukh() generated warnings!
[download]

---
demerphq
my friends call me, usually because I'm late....

---

---

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