We sometimes want to develop global function which is common in software. For example, it is a function that notifies users of errors. In that case, we can use window object.

import notify from 'path/to/notify'window.notify = notifyfunction a () {
   notify()
}
function b () {
  notify()
}

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Basically, while writing ruby codes, I avoid using inheritance because inheritance sometimes produce unnecessary tight couplings.

Example

class Vehicle   
  def start_engine
  end      def stop_engine  
  end 
end  
class Car < Vehicle   
  def drive     
    start_engine 
    stop_engine  
  end 
end

In this case, Car class knows about the codes of Vehicle class. If we create objects that don’t use an engine, it will necessary to take much time to change the codes.

Solution

We should use compositions. In other words, we should define Engine object.

class Car   
  def initialize     
    @engine = Engine.new   
  end      def drive     
    @engine.start
    @engine.stop   
  end 
end  class Engine   
  def start 
  end      def stop    
  end 
end

In this case, Engine class was separated from Car class. Moreover, it has become easy to make new objects that don’t use an engine.

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Basically, “bundle exec” command precedes rails commands. My subordinate asked me about the necessity of this command. I’m going to write it down here.

Rails has gemfile.lock file that solves dependencies among gems. When we use bundle exec command, gemfile.lock file is referred to. Instead of that, if we don’t use bundle exec command, gemfile.lock file isn’t referred to. As a result, a gem might not work properly.

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class A
  class << self
    LOGO_PATH = 'api/path'
    LOGO_WIDTH = 150
  end
end

What should we do if we want to get LOGO_PATH and LOGO_WIDTH in other places?

The solution is

A.singleton_class::LOGO_PATH => 'api/path'
A.singleton_class::LOGO_WIDTH => 150

The reference is below.

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This callback is triggered when an instance is inserted as a record and saved.

after_create_commit

This callback is triggered when an instance is inserted as a record, saved and committed. The process of commie is executed once after all processes to database finish.

We sometimes have to read library codes for curiosity or bug fixes. However, there are some techniques needed, so I’ll write them down here.

Set up path for installing gems

bundle config set path ‘vendor/bundle’ —- local

Codes of library become visible in our projects and it has become possible to insert pry codes into libraries.

Find where methods are defined

class Book
  def read
  end
end> Book.new.method(:read).source_location
=> ['book.rb', 2]

Use debuggers

・binding.irb

・binding.pry

・byebug

Find a caller

・puts caller

class BooksController < ApplicationController
  def index
    puts caller
  end
end
# caller is default in Ruby

・backtrace(this is in byebug)

That’s all! Make debugging more effective by using techniques above.

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