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
Write you own context manager
A sample context manager to open and close a file. Similarly, you can write your own.
def open(filename)
f = File.open(filename)
close_file = finish do |file|
file.close
end
[f, close_file]
end
Calling the context manager
require 'context_manager'
with open('filename.txt') do |file|
file.read
end
Examples
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
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