How does Ruby recognize elements in '.each' function?

Question

This is a general question. Let's say I have following code:
```ruby
line_count = 0
File.open("text.txt").each {|line| line_count += 1}
puts line_count
```
Now I've used the code an miraculously it does count the lines. That being said, I don't get how it knows to count them. I can replace 'dogs' for 'line' and it will still count the lines. Furthermore, opening a random text file, how does Ruby choose to break it into lines in general and not, per se, words? For a '.each' function that seems more reasonable to me. Again, very n00bish here, so thank you for your patience. 
Thanks!
Andrew Carr

Geoff Parsons · Accepted Answer

File.open returns an IO object. If we look at the IO documentation for the each method (http://www.ruby-doc.org/core-2.2.0/IO.html#method-i-each) you can see that it:
Executes the block for every line in ios, where lines are separated by sep. ios must be opened for reading or an IOError will be raised.
In your case the line variable in your block is just where you are choosing to store the line when it is yielded to the block. That's why changing the name to 'dogs' didn't matter. If you'd like to be more specific in your code you could also use #each_line (http://www.ruby-doc.org/core-2.2.0/IO.html#method-i-each_line). Each class, including those you create, can define how they handle enumerating with #each should they choose to implement it at all. 
Also as a shortcut you could use the following:
ruby
  line_count = File.open('text.txt').each_line.count

Andrew Carr · Answer

Thanks!

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Andrew Carr

Andrew Carr

How does Ruby recognize elements in '.each' function?

2 Answers

Geoff Parsons

Geoff Parsons

Andrew Carr

Andrew Carr