How do I use hash keys as methods on a class?

Question

I have a class and a hash. How can I get the members of the hash to dynamically become methods on the class with the key as the method name?

class User
  def         


        

Answer 1

Actually severin have a better idea, just because usage of method_missing is a bad practice, not all the time, but most of it.

One problem with that code provided by severin: it returns value that have been passed to initializer, so you cannot change it. I suggest you a little different approach:

class User < Hash
  def initialize(attrs)
    attrs.each do |k, v|
      self[k] = v
    end
  end

  def []=(k, v)
    unless respond_to?(k)
      self.class.send :define_method, k do
        self[k]
      end
    end

    super
  end
end

Lets check it:

u = User.new(:name => 'John')
p u.name
u[:name] = 'Maria'
p u.name

And also you can do it with Struct:

attrs = {:name => 'John', :age => 22, :position => 'developer'}
keys = attrs.keys

user = Struct.new(*keys).new(*keys.map { |k| attrs[k] })

Lets test it:

p user
p user.name
user[:name] = 'Maria'
p user.name
user.name = 'Vlad'
p user[:name]

Or even OpenStruct, but be careful it will not create method if it already have it in instance methods, you can look for that by using OpenStruct.instance_methods (because of type is used, I'm now using second approach):

attrs = {:name => 'John', :age => 22, :position => 'developer'}
user = OpenStruct.new(attrs)

Yep, so easy:

user.name
user[:name] # will give you an error, because OpenStruct isn't a Enumerable or Hash