How can I execute a block to populate a variable only if the variable is blank?

Question

I have some instance methods in a class that must be called in a sequence. The failure of any method in a sequence will require the previous method to be re-called. I'm storing the result of each successful method call in a class variable:

class User
  @@auth_hash = {}
  def get_auth_token
    result = MyApi.get_new_auth_token(self) if @@auth_hash[self]['auth_token'].blank?
    if result['Errors']
      raise Exception, "You must reauthorize against the external application."
    else
      @@auth_hash[self]['auth_token'] = result['auth_token']
    end
    @@auth_hash[self]['auth_token']
  end
  def get_session_id
    result = MyApi.get_new_session_id if @@auth_hash[self]['session_id'].blank?
    if result['Errors']
      get_auth_token
      # Recursion
      get_session_id
    else
      @@auth_hash[self]['session_id'] = result['session_id']
    end
    @@auth_hash[self]['session_id']
  end
end

I would like to get rid of those conditionals, but don't know how to perform the block only if there are errors present in the returned hash.

Answer 1

This whole method requires a rewrite...but to answer your question, why wouldn't the following work?

my_proc = ->(){ fill_me_with_something }
my_var ||= my_proc.call

raise StandardError if my_var.nil?

Editing my answer to better answer the question...The syntax:

 my_proc  =   ->(a,b){ a + b } 

Is another way to express a block, for all intents and purposes:

 my_proc(1, 5)   #=> 6

You can also express Procs in this format:

 my_proc = Proc.new{ |a, b| a + b }

The advantage of using a Proc is that you can set your block-like behavior to some variable, and then invoke call on that proc whenever you want, which, in your case, is when some other variable is blank.