Q:

Pass a constant name to another method

I have read about sending method names as parameters in ruby, however in my case I want to allow the user to select a Digest format and use the answer to set the digest type:
def hash_digest(file, argument)
    format = Digest::argument.new  #using the argument here

    ...

end

hash_digest(filename, :MD5)

I have tried:
def hash_digest(file, argument)
    format = Digest::send(argument).new 
    ...
end

hash_digest(filename, :MD5)

But I get a no method `md5' error, despite MD5 being a valid algorithm in the Digest method.  The exact error is: 
send': undefined method MD5' for Digest:Module (NoMethodError) –

Is this possible in ruby?

A:

I believe this works:
require 'digest'

def hash_digest(file, digest_algorithm)
    format = Digest.const_get(digest_algorithm).new
end

hash_digest('test', 'SHA256')

Also since the number of options is fairly small you could always just use a case statement:
require 'digest'

def hash_digest(file, digest_algorithm)
    format = case digest_algorithm
             when 'HMAC'   then Digest::HMAC.new 
             when 'MD5'    then Digest::MD5.new 
             when 'RMD160' then Digest::RMD160.new
             when 'SHA1'   then Digest::SHA1.new  
             when 'SHA256' then Digest::SHA256.new 
             when 'SHA384' then Digest::SHA384.new
             when 'SHA512' then Digest::SHA512.new  
             end
end

hash_digest('test', 'SHA256')

