How to detect if ruby code is invoked via Ruby on Rails - ruby-on-rails

Question

I wrote a small .rb tool that used the "blank?" method. I want my program to continue to work if invoked directly by ruby. I Monkey Patched Object with code below but I don't want to monkey patch when running under Rails. What can I do?
class Object
def blank?
respond_to?(:empty?) ? (respond_to?(:strip) ? strip.empty? : !!empty?) : !self
end
end

Answer 1

The first thing to keep in mind is that monkey-patching a class directly — that is, opening a class to define a new method — is discouraged. It works, but it's not very flexible and it's considered a code smell.
A more sensible approach to monkey-patching is to define your methods in a mixin and then including it in a class.
This also allows you to conditionally include the mixin. For example, a common requirement in Ruby Gems is to only implement or define something if another library is (already) loaded. A common way to do this is to check if a constant from that library is defined. For example, in your case you could do this:
module PresenceExtensions
def blank?
respond_to?(:empty?) ? (respond_to?(:strip) ? strip.empty? : !!empty?) : !self
end
end
unless Module.const_defined?("Rails") || Object.method_defined?(:blank?)
Object.include PresenceExtensions
end
Another common technique is to try to load a gem and then add your alternative monkey-patch only if the gem is not available:
begin
require "active_support/core_ext/object/blank"
rescue LoadError
Object.include PresenceExtensions
end
This technique has the advantage that will tell you immediately if the gem is not available, so that you don't have to worry about load order.

Answer 2

Rails by default should not load a file at runtime unless it is expected to through some kind of configuration either by default or an initializer etc. If this class definition just sits inside your lib/monkey.rb for example, Rails won't auto-load it unless you tell it to.
You can test this out in your rails console if you are using pry.
Just do:
rails c
# inside your console:
show-method Object.blank?
# this should show you the actual method definition which should be somthing
# like:
From: /Users/myself/.rvm/gems/ruby-2.5.1/gems/activesupport-4.2.10/lib/active_support/core_ext/object/blank.rb # line 16:
Owner: Object
Visibility: public
Number of lines: 3
def blank?
respond_to?(:empty?) ? !!empty? : !self
end
But if rails had loaded your lib file, you would see instead that definition which you can force in the console with require
require './lib/monkey.rb'
show-method Object.blank?
From: /Users/myself/some/rails/project/lib/monkey.rb # line 2:
Owner: Object
Visibility: public
Number of lines: 4
def blank?
puts "this is a monkey patch"
respond_to?(:empty?) ? (respond_to?(:strip) ? strip.empty? : !!empty?) : !self
end