Dario Daic

dariodaic5.1@gmail.com

>>  dariodaic

/

Worth as a criteria

Enumerable module

few_iterators = [:map, :select, :sort, :inject, :count]

for iterator in few_iterators do
  puts "There is a 'for' loop in Ruby!? ^^"
end

• it's a module

• it defines a bunch of iterators

• it requires host class to define an #each method

Enumerator class

enumerator = Enumerator.new do |yielder|
  yielder.yield 1
  yielder.yield 2
  yielder.yield 3
end

enumerator.map { |n| n * 100 }

• it's a class

• it has objects

• it includes Enumerable

• it requires external collection

iterate (ˈɪtəˌreɪt)

- to do something over again or repeatedly

enumerate (ɪˈnjuːməˌreɪt)

- to determine the number of; count

VS

iterator

METHOD

VS

enumerator

INSTANCE

3 ways to create an enumerator:

• Enumerator#new()
• Enumerator#new /w block
• #to_enum & #enum_for
• via blockless iterator

What does an enumerator require to function?

• must hook up to an external collection
• uses a default method - #each

#learnbydoing

What does it provide in return?

• enables both internal and external iteration
• lets us economize on object creation when chaining methods
• endows collections it hooks up on with enumerability
• protects objects from modification

What gotchas you should watch out for?

• it can un-override methods of a class
• it can be confusing to read if not understood correctly
• "enumerator literacy" - David A. Black

External iteration

Way of manipulating execution of internal iteration.

• #next - get next value that is going to be yielded
• #feed - return specified value from a yield
• #rewind - return internal iterator to the beginning
• StopIteration#result - fetch a return value of internal iteration

Lazy enumerator

• Ordinary enumerator is eager
• Lazy enumerator is, well...lazy
• created using #lazy or #lazy_enum
• enumeration has to be forced
• uses Generator and Yielder differently

Conclusion(s)

References

Benjamin Tan Wei Hao:

http://www.sitepoint.com/implementing-lazy-enumerables-in-ruby/

Pat Shaughnessy:

http://patshaughnessy.net/2013/4/3/ruby-2-0-works-hard-so-you-can-be-lazy

David A. Black:

https://www.manning.com/books/the-well-grounded-rubyist-second-edition