Context Managers

Python like context mangers in Ruby. Context managers allow you to allocate and release resources precisely when you want to.

Install

gem install context_manager

Use in-built context manager methods

1. Open a file

It will open the file passed as parameter and close it automatically.

with cm_fopen('some_file.txt') do |file|
    puts file.read
end

More context manager methods are coming soon. If you have any suggestions for any context manager method raise an enhancement issue.

Write you own context manager

1. Connect to DB

def connect_db
  # harcoding DB values to keep the example simple
  conn = Mysql2::Client.new(
    host: 'localhost',
    username: 'root',
    password: 'root',
    database: "my_database"
  )
  close_conn = finish { |conn| conn.close }
  [conn, close_conn]
end

Call with the DB context manager

with connect_db do |conn|
  result = conn.query("select * from users limit 1")
  result.first
end

2. Read from a file and write to other file

You can even write a nested context manager. For example, If you want to read contents from a file and write it to some other file.

Context manager that opens file in read mode

def open(filename)
  f = File.open(filename)
  close_file = finish { |file| file.close }
  [f, close_file]
end

Context manager that opens file in write mode

def write(filename)
  f = File.open(filename, 'w')
  close_file = finish { |file| file.close }
  [f, close_file]
end

Call write context manager inside read

with open('read_from_file.txt') do |read_file|
  with write('write_to_file.txt') do |write_file|
    write_file.write read_file.read
  end
end