How does Rails params parse hash from string - ruby-on-rails

Question

I'm learning Ruby on Rails and got curious how the params method works. I understand what it does, but how?
Is there a built-in method that takes a hash string like so
"cat[name]"
and translates it to
{ :cat => { :name => <assigned_value> } }
?
I have attempted to write the params method myself but am not sure how to write this functionality in ruby.

Answer 1

The GET parameters are set from ActionDispatch::Request#GET, which extends Rack::Request#GET, which uses Rack::QueryParser#parse_nested_query.
The POST parameters are set from ActionDispatch::Request#POST, which extends Rack::Request#POST, which uses Rack::Multipart#parse_multipart. That splays through several more files in lib/rack/multipart.

Answer 2

Here is a reproduction of the functionality of the method (note: this is NOT how the method works). Helper methods of interest: #array_to_hash and #handle_nested_hash_array
require 'uri'
class Params
def initialize(req, route_params = {})
#params = {}
route_params.keys.each do |key|
handle_nested_hash_array([{key => route_params[key]}])
end
parse_www_encoded_form(req.query_string) if req.query_string
parse_www_encoded_form(req.body) if req.body
end
def [](key)
#params[key.to_sym] || #params[key.to_s]
end
def to_s
#params.to_s
end
class AttributeNotFoundError < ArgumentError; end;
private
def parse_www_encoded_form(www_encoded_form)
params_array = URI::decode_www_form(www_encoded_form).map do |k, v|
[parse_key(k), v]
end
params_array.map! do |sub_array|
array_to_hash(sub_array.flatten)
end
handle_nested_hash_array(params_array)
end
def handle_nested_hash_array(params_array)
params_array.each do |working_hash|
params = #params
while true
if params.keys.include?(working_hash.keys[0])
params = params[working_hash.keys[0]]
working_hash = working_hash[working_hash.keys[0]]
else
break
end
break if !working_hash.values[0].is_a?(Hash)
break if !params.values[0].is_a?(Hash)
end
params.merge!(working_hash)
end
end
def array_to_hash(params_array)
return params_array.join if params_array.length == 1
hash = {}
hash[params_array[0]] = array_to_hash(params_array.drop(1))
hash
end
def parse_key(key)
key.split(/\]\[|\[|\]/)
end
end