A further level of abstraction and optimization can be provided by custom-compiling a subroutine optimized to perform the necessary task: 
use strict;
use UNIVERSAL 'isa';

sub build_deep_sub {
  my %options = @_;
  
  my $sub = q/ sub / . ( $options{proto} ? "($options{proto})" : '' ) 
+. q/ {
    / . ( $options{init} ) . q/
    my ( @results, %seen );
    
    while ( scalar @_ ) {
      my $target = shift;
      / . ( $options{guard} ? "next unless grep { $options{guard} } \$
+target;" : "" ) . q/
      push @results, / . ( $options{map} ) . q/ $target;
      
      / . ( $options{post_order} ? 'push' : 'unshift' ) . q/  @_,
      / . ( $options{guard} ? "  grep { $options{guard} }" : "" ) . q/
    $seen{$target} ++        ? ()       :    
      isa($target, 'HASH')   ? %$target :
      isa($target, 'ARRAY')  ? @$target :
      isa($target, 'REF')    ? $$target :
      isa($target, 'SCALAR') ? $$target : ();
    }
    @results;
  } /;
  eval $sub or die "$@: $sub";
}

my $type_search = build_deep_sub( init => 'my $type = shift;', map => 
+'grep isa( $_, $type ), ', guard => 'ref($_)' );

my @loggers = $type_search->( 'Log', $target );

[download]

The speed improvement of eliminating a round of subroutine calls will outway the one-time cost of the string eval unless your data structure to be searched is very small.

A library based on this approach could pre-generate a number of generally useful subroutines: 

  *{'deep_walk'} = build_deep_sub();
  *{'deep_map'} = build_deep_sub( init => 'my $test = shift;', map => 
+'map $test->($_),' );
  *{'deep_grep'} = build_deep_sub( init => 'my $test = shift;', map =>
+ 'grep $test->($_),' );
  *{'deep_grep_refs'} = build_deep_sub( init => 'my $test = shift;', m
+ap => 'grep $test->($_),', guard => 'ref($_)' );
  *{'deep_grep_type'} = build_deep_sub( init => 'my $type = shift;', m
+ap => 'grep isa( $_, $type ), ', guard => 'ref($_)' );

[download]

(For what it's worth, the prototypes generated above don't seem to be quite right, but I'm sure that could be figured out with a bit of experimentation.)

In reply to Re^4: searching for an object reference by simonm
in thread searching for an object reference by Anonymous Monk

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