elixir mix app cannot understand clearly - erlang

Question

i try to work with elixir.
it's bit hard to understand about application.ex
defmodule PluralsightTweet.Application do
# See http://elixir-lang.org/docs/stable/elixir/Application.html
# for more information on OTP Applications
#moduledoc false
use Application
def start(_type, _args) do
import Supervisor.Spec, warn: false
# Define workers and child supervisors to be supervised
children = [
# Starts a worker by calling: PluralsightTweet.Worker.start_link(arg1, arg2, arg3)
worker(PluralsightTweet.TweetServer, [])
]
# See http://elixir-lang.org/docs/stable/elixir/Supervisor.html
# for other strategies and supported options
opts = [strategy: :one_for_one, name: PluralsightTweet.Supervisor]
process = Supervisor.start_link(children, opts)
PluralsightTweet.Scheduler.schedule_file("* * * * *", Path.join("#{:code.priv_dir(:pluralsight_tweet)}",
"sample.txt"))
process
end
end
i'm following pluralsight elixir tutorial
this is scheduler to tweet text in every minute from reading text file
task is success but doesn't have crystal clear ideal about the process
can some one please explain whats happening inside application.ex
run as a supervisor app

Answer 1

use Application
This line means the current module is the entrance of an application. Such module can be configured in the mix.exs to be started as a unit.
# Inside mix.exs
def application do
[
extra_applications: [:logger],
mod: {PluralsightTweet.Application, []} # <-- this line
]
end
The start function
This function is the callback when the application starts up. You can consider it as the main function in some other languages.
import Supervisor.Spec, warn: false
It just lets you omit the module name when you call worker, supervisor and supervise. The warn: false part suppresses warning even if you don't call any of those functions.
children = [worker(PluralsightTweet.TweetServer, [])]
This line specifies the child processes that your application supervises. Note that at this point, the child processes are not spawned yet.
The worker(mod, args) just defines a worker spec that will be started later. The args will be passed to the mod's start_link function when starting the worker.
opts = [strategy: :one_for_one, name: PluralsightTweet.Supervisor]
The supervisor options.
See strategies documentation for the meaning of strategy: :one_for_one and other strategies.
Since you have only one worker, all strategies except :simple_one_for_one works pretty the same.
The tricky part is name: PluralsightTweet.Supervisor. You may wonder where did the module PluralsightTweet.Supervisor come from. The fact is that it is NOT a module. It's only an atom :"Elixir.PluralsightTweet.Supervisor", which serves as the name of the supervisor process.
Supervisor.start_link(children, opts)
Now the supervisor process and its child processes are spawned.