local variable shadows ivar

local variable shadows ivar.rb

class Foo
  attr_accessor :params

  def initialize(params)
    @params = params
  end

  def process(params)
    puts "====> before: #{params.inspect}"
    params.merge!(local: "modifications")
    puts "====> after: #{params.inspect}"
  end
end

params = { initial: "hash" }
foo = Foo.new(params)
puts "====> initial global: #{params.inspect}"
puts "====> initial in foo: #{foo.params.inspect}"

foo.process(something: "new")

puts "====> foo: #{foo.params.inspect}"

__END__

ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.3.0]

====> initial global: {:initial=>"hash"}
====> initial in foo: {:initial=>"hash"}
====> before: {:something=>"new"}
====> after: {:something=>"new", :local=>"modifications"}
====> foo: {:initial=>"hash"}

usecase is not about shadowing, but about modifying what is passed.

class Foo
  attr_accessor :params

  def initialize(params)
    params.merge!(hello: 'world')
  end
end

params = { initial: "hash" }
puts "====> initial global: #{params.inspect}"
foo = Foo.new(params)
puts "====> initial in foo: #{foo.params.inspect}"
puts "====> global: #{params.inspect}"