Initialize a Ruby class from an arbitrary hash, but only keys with matching accessors

Question

Is there a simple way to list the accessors/readers that have been set in a Ruby Class?

class Test
  attr_reader :one, :two

  def initialize
    # Do someth         


        

Answer 1

Try something like this:

class Test
  attr_accessor :foo, :bar

  def initialize(opts = {})
    opts.each do |opt, val|
      send("#{opt}=", val) if respond_to? "#{opt}="
    end
  end
end

test = Test.new(:foo => "a", :bar => "b", :baz => "c")

p test.foo # => nil
p test.bar # => nil
p test.baz # => undefined method `baz' for # (NoMethodError)

This is basically what Rails does when you pass in a params hash to new. It will ignore all parameters it doesn't know about, and it will allow you to set things that aren't necessarily defined by attr_accessor, but still have an appropriate setter.

The only downside is that this really requires that you have a setter defined (versus just the accessor) which may not be what you're looking for.