Bundler - 无法加载2个不同版本的完全相同的gem？

Question

I've watched this presentation on how Bundler works and one of the reasons Bundler was invented was to solve 'activation errors', for eg:

LoadError: can't activate rack (~> 1.0.0, runtime) for ['actonpack-2.3.5'], already activated rack-1.1.0 for ['thin-1.2.7']

Does this basically means that you cannot run 2 different versions of the exact same gem at a same time, in a single Ruby process?

Answer 1

You cannot have two different versions of the same gem loaded the same program, because they could conflict and override each other's methods. For example, suppose you have a gem which contains the following:

# In gem version 1.0
class AneMaria
  def self.name
    "Ane"
  end
end

######

# In gem version 2.0
class AneMaria
  def self.name
    "Maria"
  end
end

And then in your code, if you call AneMaria.name , what should it return??

One of the reasons tools like bundler were created was to prevent this from happening accidentally -- so no, you cannot specify 2 different versions of a gem to load simultaneously. (Also, I don't think you'll ever want to do that!)

See also this post , which explains things a little more.