qs_to_hash.rb

# Today's little useless tidbit converts a url's query string into a hash 
# set of k/v pairs in a way that merges duplicates and massages empty 
# querystring values

def qs_to_hash(query_string)
  keyvals = query_string.split('&').inject({}) do |result, q| 
    k,v = q.split('=')
    if !v.nil?
       result.merge({k => v})
    elsif !result.key?(k)
      result.merge({k => true})
    else
      result
    end
  end
  keyvals
end

qs_to_hash("a=b&b=c&c=d")   # {a=>b, b=>c, c=>d}
qs_to_hash("a=b&b=c&c")     # {a=>b, b=>c, c=>true} nil becomes true
qs_to_hash("a=b&b=c&a=d")   # {a=>d, b=>c} last declaration wins
qs_to_hash("a=b&b=c&a")     # {a=>b, b=>c} nils don't override set vals

# Now, of course Rails's implementation is much smarter than this... 
# but you never know.