Incrementing letters using .next

Question

def home
  letter = 'A'
  @markers = Location.all.to_gmaps4rails do |loc, marker|
    marker.infowindow render_to_string(partial: '/locations/info', 
                                       locals: {object: loc})
    marker.picture({picture: "http://chart.apis.google.com/chart?chst=d_map_pin_letter&chld=#{letter.next!}|9966FF|000000",
                    width: 32,
                    height: 32,
                    shadow_picture: "http://chart.apis.google.com/chart?chst=d_map_pin_shadow",
                    shadow_width: 110,
                    shadow_height: 110,
                    shadow_anchor: [17,36]})
    marker.title "Title - #{loc.name}"
    marker.sidebar render_to_string(partial: '/locations/sidebar', 
                                    locals: {object: loc})
    marker.json({id: loc.id})
  end
end

Cool stuff. So this works. It cycles through the do loop and increments the letter. Problem is, it starts at B. I tried using just letter in the picture, then at the end using letter.next!, and even letter = letter.next, but gmaps throws an error at me.

Is there a way to assign something besides 'A' to letter?

Answer 1

This works, but I'll second @patrick-oscity in that it is arguably obscure:

letter = '@'
letter.next! #=> "A"

Another solution is mutating the letter at the end of the loop, after using it.

This snippet:

letter = 'A'

1.upto(5) do
  puts letter
  letter.next!
end

... produces this output:

A
B
C
D
E

Answer 2

Well technically, '@' is the predecessor of 'A', because the ASCII value of '@' is 64 and the value of 'A' is 65. Observe:

'A'.codepoints.first
#=> 65

'A'.codepoints.first - 1
#=> 64

('A'.codepoints.first - 1).chr
#=> "@"

('A'.codepoints.first - 1).chr.next
#=> "A"

in that sense:

'@'.next == 'A'
#=> true

but i strongly discourage the use of black magic™. Use something like @nicooga's approach in real code.