TIL, 2017-09-18

• More refactoring lessons.
• ls -R to see all files recursively.
• touch on an existing file will change the access time.
• Hard link, must be same physical drive.
• Symbolic link: cp -s file file2, and ln -s file file2.
• file myfile determine the kind of file.
• tail is used to view the last 10 lines of a file.
• head is used to view the first 10 lines of a file.
• ps aux to list the currently running processes.
• top -o cpu to list processes by CPU.
• pkill to kill a process, xkill to kill any non-responsive window.
• Postgres has a server.log which can only be deleted if Postgres is not running anymore.

React

• yarn is Facebook’s answer to npm.
• https://github.com/facebookincubator/create-react-app/ as the app template.
• Create an .env file in the base directory.
• yarn add react-router to add the react router.
• This is sad, but declaring a function in JavaScript: aw = function() { 1 + 1 }.

Destroy All Software, Collapsing Services into Values and How and Why To Avoid Nil

class Subscription < Struct.new(:id, :type)
  attr_reader :allow_export
  alias_method :allow_export?, :allow_export

  def initialize(id, type)
    @id = id
    @type = type
    @allow_export = active? && type == 'business'
  end

  def active?
    id.present?
  end
end

• Resolving nils–introduce a new domain concept (Null Object?)