attr_accessor won't work when used in procs

Question

I wrote the following snippet to download some files I need to.

require 'open-uri'

MEGABYTE = 1024.0 * 1024.0

def bytes_to_megabytes(bytes)
  bytes / MEGABYTE
end

class Downloader
  class << self
    attr_accessor :size

    def get(resource)
      open(resource,
         content_length_proc: proc do |t|
           size = bytes_to_megabytes(t).round
           puts "Total size is: #{size}"
         end,
         progress_proc: proc do |step| 
           # size won't print here!
           puts "Downloading #{bytes_to_megabytes(step).round} out of #{size}"
         end ) 
    end
  end
end

Problem is the total size won't print on the last line even though it has already been set in content_length_proc.

Why is this happening?

Answer 1

even though it has already been set in content_length_proc

No, it hasn't been set. You set a local variable size there, not the accessor. Rookie mistake. Change to this:

self.size = bytes_to_megabytes(t).round