# let array handle context.
    # list of items in list context, count of items in scalar.
    sub find_things {
       my( $storage, $criteria ) = @_;
       my @things = $storage->lookup( $criteria );
       @things
    }

    # let grep handle context.
    # list of items in list context, count of items in scalar.
    sub matching_things {
       my( $storage, $pat ) = @_;
       grep /$pat/, $storage->things()
    }

##</code><code>##

    # list of items in list context, first item in scalar.
    sub matching_things {
       my( $input_iter, $pat ) = @_;
       my @things;
       while ( <$input_iter> ) {
           /$pat/ or next;
           wantarray or return $_;
           push @things, $_;
       }
       @things
    }