.Cycle In Ruby
What is it? And how do you use it?
29 April 2015
Enumerable#cycle - “Calls block for each element of enum repeatedly n times or forever if none or nil is given.” (Rubydocs) If this definition sounds confusing, don’t worry, this essay will explain it.
Understanding what Enumerable#cycle (or .cycle) does in Ruby requires you to understand Enumerable#each (or .each).
.each will grab each item within an array and shove it into a ‘block’ (code placed within brackets). For example:
example_array = [0,1,2]
| example_array.each { | x | puts x*2 } |
=>0, 2, 4 </code>
But what if I wanted to use .each multiple times? Well, you would use .cycle instead!
example_array.cycle(2) { |x| puts x*2 }
=>0, 2, 4, 0, 2, 4 </code>
You must specify a number for .cycle , otherwise, Ruby will not know when to stop.
example_array.cycle { |x| puts x*2 }
=>0, 2, 4, 0, 2, 4, 0, 2, 4, 0, 2, 4, 0, 2, 4…
And so on…for infinity. </code>
…Sometimes, you may want an endless sequence like this. If you want only see one number at a time in this endless sequence, you will need to save “example_array.cycle” in a variable, and then use the ‘.next’ method on that variable.
nextnumber = example_array.cycle { |x| puts x*2 }
nextnumber.next => 0
nextnumber.next => 2
nextnumber.next => 4
nextnumber.next => 0
nextnumber.next => 2
And so on…for infinity. </code>