Question

I wrote some code:

output = File.open(text_file).collect.reverse.join("<BR>")

It seems to work okay on 1.8.7 but throws the error

NoMethodError - undefined method 'reverse' for #<Enumerator: #<File:C:\EduTester\cron\rufus.log>:collect>:

on 1.9.1 (ruby 1.9.3p194 (2012-04-20) [i386-mingw32])

Does somebody know why this happens and how to fix this? (Why is of most interest to me.)

Answer 1

First how to fix it – you should be doing this:

output = File.open(text_file).to_a.reverse.join("<BR>") 

This will work on either version of Ruby. Basically you need to turn the file into an array of lines (with .to_a) before reversing them and adding line breaks.

In terms of the why (this gets a little technical): File mixes in the Enumerable module, which gives it methods like collect. Now in Ruby 1.87, if you called Enumberable.collect without a block it would return an Array. But in 1.9, it returns an Enumerator – which doesn’t respond to the reverse method.

Here are the 2 versions of the method in question:

http://ruby-doc.org/core-1.8.7/Enumerable.html#method-i-collect
http://ruby-doc.org/core-1.9.3/Enumerable.html#method-i-collect

So basically before 1.9 .collect was a (hacky) equivalent to .to_a. But always use .to_a to turn something into an array.