Merge and Reverse Merge

Merge in Ruby works like this:

> options = { buy: true }
 => {:buy=>true}
> options.merge! when: :tomorrow
 => {:buy=>true, :when=>:tomorrow}
> options
 => {:buy=>true, :when=>:tomorrow}
> options.merge! buy: false
 => {:buy=>false, :when=>:tomorrow}
> options
 => {:buy=>false, :when=>:tomorrow}
> options.merge! :when => :today
 => {:buy=>false, :when=>:today}

Reverse Merge in Rails works like this:

 rails c
Loading development environment (Rails 5.0.0.beta3)
 > options = { buy: true }
 => {:buy=>true} 
 > options.reverse_merge! when: :tomorrow
 => {:buy=>true, :when=>:tomorrow} 
 > options
 => {:buy=>true, :when=>:tomorrow} 
 > options.reverse_merge! buy: false
 => {:buy=>true, :when=>:tomorrow} 
 > options
 => {:buy=>true, :when=>:tomorrow} 
 > options.reverse_merge! :when => :today
 => {:buy=>true, :when=>:tomorrow}