Ruby

Tips

Let’s say we want to find numbers that are divisible by 19 and 23.

infinite_range = (1..Float::INFINITY)

Calling select on infinite range will hang forever because select is eager:

e = infinite_range.select {|n| n % 19 == 0 && n % 23 == 0 }

Adding lazy will return an Enumerator::Lazy instance:

e = infinite_range.lazy.select {|n| n % 19 == 0 && n % 23 == 0 }

Now we can call next on the enumerator and select will be evaluated lazily:

e.class #=> Enumerator::Lazy
e.next  #=> 437
e.next  #=> 874