Digest::Base

ruby-talk
1

I wish to write one method to work with all classes in Digest::Base without repeatedly writing the same code.

def setup(file, hash_type)

   # hash_type could be MD5, SHA1, SHA256, etc.

   Digest::hash_type.new
   Hash the file.

end

The above example is what I'd like to be able to do, but it does not work. I cannot insert 'hash_type' into the method in this manner. Trying to do so produces errors. I can do a bunch of conditionals like this:

def setup(file, hash_type)

   if hash_type == MD5
     Digest::MD5.new
     Hash the file.

   elsif hash_type == RMD160
     Digest::RMD160.new
     Hash the file.

   else....
     ....

end

But then, I begin repeating myself. Any tips on making this work with fewer lines of code?

Thanks!

2

Check out Module#const_get in ri:

Digest.const_get('MD5').new

3

How about this:

$ cat digest.rb
require 'digest/md5'
require 'digest/sha1'
require 'digest/sha2'
require 'digest/rmd160'

def hash_file(file, hash_kind)
   digest = Digest.const_get(hash_kind.to_s.upcase).new
   open(file, 'rb') do |f|
     while (chunk = f.read(1))
       digest.update(chunk)
     end
   end
   digest
end

puts "RMD160: #{hash_file(__FILE__, :rmd160)}"
puts "MD5: #{hash_file(__FILE__, :md5)}"
puts "SHA1: #{hash_file(__FILE__, :sha1)}"
puts "SHA256: #{hash_file(__FILE__, :sha256)}"

$ ruby digest.rb
RMD160: a99c2c1919b289412a98dc4562598d904e2a5750
MD5: 0a35b2d64cc5201314b691f3c8588ac6
SHA1: f47b890ec66801e1f24956214d8a6f13c7f8daac
SHA256: bda670c53c5ff548a88f274ce17493adc0c229e32c221990e0c779c881425886

-- Daniel

···

On Mar 20, 2006, at 2:28 PM, rtilley wrote:

I wish to write one method to work with all classes in Digest::Base without repeatedly writing the same code.

4

rmagick@gmail.com wrote:

Check out Module#const_get in ri:

Digest.const_get('MD5').new

That's great... Thanks for the tip!

5

Daniel Harple schrieb:

I wish to write one method to work with all classes in Digest::Base
without repeatedly writing the same code.

How about this:

$ cat digest.rb
require 'digest/md5'
require 'digest/sha1'
require 'digest/sha2'
require 'digest/rmd160'

def hash_file(file, hash_kind)
  digest = Digest.const_get(hash_kind.to_s.upcase).new
  open(file, 'rb') do |f|
    while (chunk = f.read(1))
      digest.update(chunk)
    end
  end
  digest
end

puts "RMD160: #{hash_file(__FILE__, :rmd160)}"
puts "MD5: #{hash_file(__FILE__, :md5)}"
puts "SHA1: #{hash_file(__FILE__, :sha1)}"
puts "SHA256: #{hash_file(__FILE__, :sha256)}"

$ ruby digest.rb
RMD160: a99c2c1919b289412a98dc4562598d904e2a5750
MD5: 0a35b2d64cc5201314b691f3c8588ac6
SHA1: f47b890ec66801e1f24956214d8a6f13c7f8daac
SHA256: bda670c53c5ff548a88f274ce17493adc0c229e32c221990e0c779c881425886

-- Daniel

Quite nice. However i think const_get isn't necessary here and should be
avoided if possible. e.g.:

def hash_file(file, hash_kind)
  digest, chunk = hash_kind.new, ''
  open(file, 'rb') do |f|
    digest << chunk while f.read(4096, chunk)
  end
  digest
end

puts "RMD160: #{hash_file(__FILE__, Digest::RMD160)}"
puts "MD5: #{hash_file(__FILE__, Digest::MD5)}"
puts "SHA1: #{hash_file(__FILE__, Digest::SHA1)}"
puts "SHA256: #{hash_file(__FILE__, Digest::SHA256)}"

cheers

Simon

···

On Mar 20, 2006, at 2:28 PM, rtilley wrote: