class Rack::QueryParser::Params

def [](key)
  @params[key]
end

def []=(key, value)
  @params[key] = value
end

def initialize
  @size   = 0
  @params = {}
end

def key?(key)
  @params.key?(key)
end

key to it is non-deterministic.
getting the hash representation while another thread is adding a
through the `#[]=` method, it is not thread safe. The result of
3. Because the `Params` object's internal representation is mutable

representation, not a copy.
2. The value you get back is a reference to the internal hash

objects in order to save object allocations.
1. This method mutates the internal representation of the `Params`

Mutation warning!

purely of Ruby primitives.
(Ruby hashes) in place of the objects. The result is a hash consisting
of the same shape, but using the objects' internal representations
Recursively unwraps nested `Params` objects and constructs an object

def to_h
  @params.each do |key, value|
    case value
    when self
      # Handle circular references gracefully.
      @params[key] = @params
    when Params
      @params[key] = value.to_h
    when Array
      value.map! { |v| v.kind_of?(Params) ? v.to_h : v }
    else
      # Ignore anything that is not a `Params` object or
      # a collection that can contain one.
    end
  end
  @params
end