in reply to Re^5: the annoying keys "key" and "value"
in thread the annoying keys "key" and "value"

This is getting a little esoteric but then if esoterica is disallowed among monks where would it be allowed, pray tell? The only cases where I can imagine the keys "key" and "value" being nonpathological are in schema descriptions. Could you expand my imagination with some counter-examples?
  • Comment on Re^6: the annoying keys "key" and "value"

Replies are listed 'Best First'.
Re^7: the annoying keys "key" and "value"
by ikegami (Patriarch) on Dec 23, 2010 at 23:28 UTC

    If it's pathalogical, what would be nonpathological?

    $param->{'key'} # { key => $key, value => $value }

    is slightly clearer than

    $param->[0] # [ $key, $value ]

    and much more clearer than

    (keys(%$param))[0] # { $key => $value }

    Update: I missed this:

    The non-pathological representation would have: $hash{$key}=[$value1, $value2, $value3,...]

    But it's not true. That doesn't maintain order, so the question remains. What would be nonpathological?

      "That doesn't maintain order"

      The array has the order.

        Really? Please recreate the original from
        { a=>[1,3,5], b=>[2,4,6], }

        If you answered the following, you would be wrong.

        a=>1 a=>3 a=>5 b=>2 b=>4 b=>6

        As far as you know, the original order was

        b=>2 b=>4 a=>1 b=>6 a=>3 a=>5
Re^7: the annoying keys "key" and "value"
by Marshall (Canon) on Dec 24, 2010 at 00:21 UTC
    This is not esoteric. Let me show some data structure access examples. In the below, imagine "key" being X and "value" being Y coordinates.

    'C': #define X_coord 0 #define Y_coord 1 #define MAX_ROWS 3 /* graph is a 2-d array of ints each row has an X and a Y coordinate Normally graph would be built dynamically as an array of pointer to array. The same [x][y] syntax can be used like in a predefined array. The same [x][y] syntax works in Perl's array of references to arrays also. Although in most cases, I would consider this a "not good thing". */ for (int row =0; row <MAX_ROWS; row++) { int this_pointX = graph[row][X_coord]; int this_pointY = graph[row][Y_coord]; .... ) ########## Perl: using Array of Array, about the same as 'C' this UGLY... my $X_coord = 0; my $Y_coord = 1; foreach my $i (0..@graph-1) # forget 0..$#graph # needless use of special variable { my $this_pointX = $graph[$i][$X_coord]; my $this_pointY = $graph[$i][$Y_coord]; } ########## Perl: Better than above using Array of Array: foreach my $row (@graph) { my ($this_pointX, $this_pointY) = @$row; .... } ########## Perl: using Array of Hash: foreach my $point (@graph) # graph is Array of Hash # meaning an array of pointers # to hash tables { my $this_pointX = $point->{'X_coord'}; my $this_pointY = $point->{'Y_coord'}; .... } # there can be big advantages to avoiding this # position dependent [$index] stuff as well as the # need to pre-declare those indicies, The Perl AoH # works very well to represent some types of C 2-D arrays. # It is very easy to imagine how an implementer would # go in that direction.
    Using Array of Hash for a C 2-D array is a very reasonable thing. The C code to implement a hash table is not huge, but it is non-trivial. If the underlying data could be better represented as a Hash of Array in Perl, then fine. It is very easy to imagine how an implementer would go in the direction of Array of Hash and miss the better Perl implementation of Hash of Array.
      I'm wasn't able to locate in that example any occurrences of the keys 'key' and 'value'.
        I thought it was pretty clear: "In the below, imagine "key" being X and "value" being Y coordinates". I'm sorry that you didn't understand that. I was showing how this technique and data structure relates to other problems.