MappedOpenStruct: useful for hashes from JSON with crappy keys

mapped_open_struct.rb

require 'ostruct'

class MappedOpenStruct < OpenStruct
  MAP = {}

  def initialize(hash=nil)
    super
    add_mapped_methods
  end
  
  private
  def add_mapped_methods
    return if self.class::MAP.nil?
    
    self.class::MAP.each_pair do |key, value|
      add_mapped_method(key.to_sym, value.to_sym)
    end
  end
  
  def add_mapped_method(new_name, old_name)
    if respond_to?(old_name) && !respond_to?(new_name)
      define_singleton_method(new_name) { @table[old_name] }
    end
    
    if respond_to?("#{old_name}=") && !respond_to?("#{new_name}=")
      define_singleton_method("#{new_name}=") { |x| modifiable[old_name] = x }
    end
  end
end

class Foo < MappedOpenStruct
  MAP = {:foobie => :fb}
end

foo = Foo.new(fb: 2, df: 12)
# => #<Foo fb=2, df=12>

# Same same
foo.fb # => 2
foo.foobie # => 2
foo.foobie = 5
foo.fb # => 5

# Doesn't pollute original hash with new keys
foo.to_h # => {:fb=>5, :df=>12}

I find myself dealing with JSON APIs a lot. They often have key names which aren't very expressive or intuitive.

This trivial class gives me an object that maps better method names onto the crappy key names without polluting the underlying hash, making it easy to work with and easy to re-serialize to JSON as needed (ex. foo.to_h.to_json)

There's probably a better way to do this, but I've never found it.