Ruby CSV Converters What's Wrong

example1.rb

require 'csv'

CSV::Converters[:num2] = lambda do |num|
  puts "Converter called with #{num}"
  return num unless num.is_a?(Numeric)
  sprintf('%.2f', num)
end

CSV.instance($stdout,
             { headers: [:name, :val] , write_headers: true,
               :converters => [:num2]}) do |csv|
  csv << { name: "a", val: 1 }
  csv << { name: "b", val: 0.0 }
  csv << { name: "c", val: 6.666666666666 }
end

example1.txt

seph$ ruby --version
ruby 2.3.3p222 (2016-11-21 revision 56859) [x86_64-darwin15]

seph$ ruby /tmp/x.rb 
Converter called with name
Converter called with val
name,val
a,1
b,0.0
c,6.666666666666

example2.rb

require 'csv'

csv = CSV.instance($stdout, {
                     headers: [:name, :val],
                     write_headers: true,
                   })

csv.convert do |num|
  begin
    puts "Converter called with #{num}"
    sprintf('%.2f', num)
  rescue
    num
  end
end

csv << { name: "a", val: 1 }
csv << { name: "b", val: 0.0 }
csv << { name: "c", val: 6.666666666666 }

puts csv.converters
puts csv.converters.first.call(6.666666666)

example2.txt

seph$ ruby --version
ruby 2.3.3p222 (2016-11-21 revision 56859) [x86_64-darwin15]

seph$ ruby /tmp/x.rb 
Converter called with name
Converter called with val
name,val
a,1
b,0.0
c,6.666666666666
#<Proc:0x007fb55a93b158@/tmp/x.rb:8>
Converter called with 6.666666666
6.67