Question

#!/usr/bin/env ruby

require 'json'

class A
  def to_json(*a)
    { :a => 'a' }.to_json(*a)
  end
end

class B < A
  def to_json(*a)
    super({ :b => 'b' })
  end
end

puts B.new.to_json

produces

{"a":"a"}

How do I get it to produce

{"a":"a", "b":"b"}

in a reasonable way?

I’m using Ruby 1.9.3 and the latest json gem.

A related question is: what are the arguments *a to to_json? I’ve scoured the docs to no avail.

Answer 1

You have two hashes {:a=>'a'} and {:b=>'b'} in two classes, they’re encapsulated i.e. hidden from outside world. The only way I can see is parse the json string into hash and merge them, then convert the result to json.

class B < A
  def to_json(*a)
    JSON.parse(super).merge({:b=>'b'}).to_json
  end
end

But here will be small difference: you’re merging {:a=>'a',:b=>'b'} and got the {"a":"a","b":"b"}

*a is parameter to set options for json format