Using method callbacks in plain Ruby class - ruby

Question

I have a plain ruby class Espresso::MyExampleClass.
module Espresso
class MyExampleClass
def my_first_function(value)
puts "my_first_function"
end
def my_function_to_run_before
puts "Running before"
end
end
end
With some of the methods in the class, I want to perform a before or after callback similar to ActiveSupport callbacks before_action or before_filter. I'd like to put something like this in my class, which will run my_function_to_run_before before my_first_function:
before_method :my_function_to_run_before, only: :my_first_function
The result should be something like:
klass = Espresso::MyExampleClass.new
klass.my_first_function("yes")
> "Running before"
> "my_first_function"
How do I use call backs in a plain ruby class like in Rails to run a method before each specified method?
Edit2:
Thanks #tadman for recommending XY problem. The real issue we have is with an API client that has a token expiration. Before each call to the API, we need to check to see if the token is expired. If we have a ton of function for the API, it would be cumbersome to check if the token was expired each time.
Here is the example class:
require "rubygems"
require "bundler/setup"
require 'active_support/all'
require 'httparty'
require 'json'
module Espresso
class Client
include HTTParty
include ActiveSupport::Callbacks
def initialize
login("admin#example.com", "password")
end
def login(username, password)
puts "logging in"
uri = URI.parse("localhost:3000" + '/login')
http = Net::HTTP.new(uri.host, uri.port)
http.use_ssl = true
http.verify_mode = OpenSSL::SSL::VERIFY_NONE
request = Net::HTTP::Post.new(uri.request_uri)
request.set_form_data(username: username, password: password)
response = http.request(request)
body = JSON.parse(response.body)
#access_token = body['access_token']
#expires_in = body['expires_in']
#expires = #expires_in.seconds.from_now
#options = {
headers: {
Authorization: "Bearer #{#access_token}"
}
}
end
def is_token_expired?
#if Time.now > #expires.
if 1.hour.ago > #expires
puts "Going to expire"
else
puts "not going to expire"
end
1.hour.ago > #expires ? false : true
end
# Gets posts
def get_posts
#Check if the token is expired, if is login again and get a new token
if is_token_expired?
login("admin#example.com", "password")
end
self.class.get('/posts', #options)
end
# Gets comments
def get_comments
#Check if the token is expired, if is login again and get a new token
if is_token_expired?
login("admin#example.com", "password")
end
self.class.get('/comments', #options)
end
end
end
klass = Espresso::Client.new
klass.get_posts
klass.get_comments

Answer 1

A naive implementation would be;
module Callbacks
def self.extended(base)
base.send(:include, InstanceMethods)
end
def overridden_methods
#overridden_methods ||= []
end
def callbacks
#callbacks ||= Hash.new { |hash, key| hash[key] = [] }
end
def method_added(method_name)
return if should_override?(method_name)
overridden_methods << method_name
original_method_name = "original_#{method_name}"
alias_method(original_method_name, method_name)
define_method(method_name) do |*args|
run_callbacks_for(method_name)
send(original_method_name, *args)
end
end
def should_override?(method_name)
overridden_methods.include?(method_name) || method_name =~ /original_/
end
def before_run(method_name, callback)
callbacks[method_name] << callback
end
module InstanceMethods
def run_callbacks_for(method_name)
self.class.callbacks[method_name].to_a.each do |callback|
send(callback)
end
end
end
end
class Foo
extend Callbacks
before_run :bar, :zoo
def bar
puts 'bar'
end
def zoo
puts 'This runs everytime you call `bar`'
end
end
Foo.new.bar #=> This runs everytime you call `bar`
#=> bar
The tricky point in this implementation is, method_added. Whenever a method gets bind, method_added method gets called by ruby with the name of the method. Inside of this method, what I am doing is just name mangling and overriding the original method with the new one which first runs the callbacks then calls the original method.
Note that, this implementation neither supports block callbacks nor callbacks for super class methods. Both of them could be implemented easily though.