Pál Dávid Gergely (nightw)
DevOps Engineer interested in scaling and fault-tolerance.
Lazy Initialization Pattern in Ruby
Pal David Gergely
Statzup Kft.
@nightw17
budapest.rb - 2015. 02. 25.
What is it?
Lazy initialization of an object means that its creation is deferred until it is first used.
Why?
- Easier to read
- Faster to run
-
Uses less resources
- Including network/databases
Simple Ruby example
class Car
def passengers
@passengers ||= []
end
def add_passenger(passenger)
@passengers ||= []
@passengers.push passenger
end
end
c = Car.new
c.passengers.each do |passenger|
puts passenger
end
#=> []
c.add_passenger('Joe')
c.passengers.each do |passenger|
puts passenger
end
# ["Joe"]A bit trickier example (ActiveRecord)
class Address
def self.find_by_person(id)
puts 'Address.find_by_person has been called!'
'Sesame street 123'
end
end
class Person
def id
4 # chosen by fair dice roll, guaranteed to be random
end
def address
@address = Address.find_by_person(self.id) unless instance_variable_defined? :@address
@address
end
end
p = Person.new
puts p.address
# Address.find_by_person has been called!
# Sesame street 123
puts p.address
# Sesame street 123A true Rubyism :)
require 'bigdecimal'
def prime?(n)
return false if n < 2
(2..Math.sqrt(n)).none? {|num| n % num == 0}
end
r = 1..BigDecimal::INFINITY
r.lazy.map{|n| n**2+1}.select{|m| prime?(m)}.first(100)
#=> [2, 5, 17, 37, 101, 197, 257, 401, 577, 677, 1297, 1601, 2917, 3137, 4357, 5477, 7057, 8101,
8837, 12101, 13457, 14401, 15377, 15877, 16901, 17957, 21317, 22501, 24337, 25601, 28901, 30977,
32401, 33857, 41617, 42437, 44101, 50177, 52901, 55697, 57601, 62501, 65537, 67601, 69697, 72901,
78401, 80657, 90001, 93637, 98597, 106277, 115601, 122501, 147457, 148997, 156817, 160001,
164837, 176401, 184901, 190097, 193601, 197137, 215297, 217157, 220901, 224677, 240101, 246017,
287297, 295937, 309137, 324901, 331777, 341057, 352837, 401957, 404497, 414737, 417317, 427717,
454277, 462401, 470597, 476101, 484417, 490001, 495617, 509797, 512657, 547601, 562501, 577601,
583697, 608401, 614657, 665857, 682277, 739601]- Only in Ruby2.0+
- Math!
- "One-liner", yay!
Why not? a.k.a Problems
- Multithreaded apps?
- If you always use the object
Questions?
Pal David Gergely
Statzup Kft.
@nightw17
budapest.rb - 2015. 02. 25.
Lazy Initialization Pattern in Ruby
By Pál Dávid Gergely (nightw)
Lazy Initialization Pattern in Ruby
A short presentation held at budapest.rb in 02/2015
