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

You could override attr_reader, attr_writer and attr_accessor to provide some kind of tracking mechanism for your class so you can have better reflection capability such as this.

For example:

class Class
  alias_method :attr_reader_without_tracking, :attr_reader
  def attr_reader(*names)
    attr_readers.concat(names)
    attr_reader_without_tracking(*names)
  end

  def attr_readers
    @attr_readers ||= [ ]
  end

  alias_method :attr_writer_without_tracking, :attr_writer
  def attr_writer(*names)
    attr_writers.concat(names)
    attr_writer_without_tracking(*names)
  end

  def attr_writers
    @attr_writers ||= [ ]
  end

  alias_method :attr_accessor_without_tracking, :attr_accessor
  def attr_accessor(*names)
    attr_readers.concat(names)
    attr_writers.concat(names)
    attr_accessor_without_tracking(*names)
  end
end

These can be demonstrated fairly simply:

class Foo
  attr_reader :foo, :bar
  attr_writer :baz
  attr_accessor :foobar
end

puts "Readers: " + Foo.attr_readers.join(', ')
# => Readers: foo, bar, foobar
puts "Writers: " + Foo.attr_writers.join(', ')
# => Writers: baz, foobar