gem 'promise.rb' leads to "undefined method `arity' for nil:NilClass"

[Rupert Meese]

Hi.

Installing as described (in my case with bundler gem 'promise') succeeds but installs the wrong gem - i.e. it installs this older and completely different promises library: https://github.com/bhuga/promising-future

Since the install appears to succeed the mistake is not apparent until you try to use the library - at which time Promise.new fails with the runtime exception:

undefined method `arity' for nil:NilClass

[Rupert Meese]

My Mistake:

gem 'promise.rb' works fine as documented. gem 'promise' leads to the error. Probably worth leaving in in case anyone does the same.