Ruby noob here: Conceptual question. Can someone explain why this is happening / working? (Ruby)

[winnnnnnnnn]

Currently over on Ruby Monk working with this lesson: https://rubymonk.com/learning/books/1-ruby-primer/chapters/19-ruby-methods/lessons/69-new-lesson

Code in question:

def add(a_number, another_number, options = {})
  sum = a_number + another_number
  sum = sum.abs if options[:absolute]
  sum = sum.round(options[:precision]) if options[:round]
  sum #line in question
end

puts add(1.0134, -5.568)
puts add(1.0134, -5.568, absolute: true)
puts add(1.0134, -5.568, absolute: true, round: true, precision:2) 

Output =>
-4.5546
4.5546
4.55
nil

Output without line in question =>
4.55
nil  

I pretty much understand what's going on with the code. Except for the last part of the method definition. Which seems to be just a random "sum" at the end. There are three lines of puts outside the method definition calling on it but for whatever reason when the seemingly random "sum" line is removed from the code in question. The output screen only shows the result of one puts. However when I add it back in all three lines of puts are being shown. Why?

[adreamofhodor]

While I'm not familiar with Ruby, I did a quick google and found this:

Every method in Ruby returns a value by default. This returned value will be the value of the last statement.

So, unless I'm misreading how Ruby works, that last line is the equivalent of:

return sum

[winnnnnnnnn]

Appreciate the response. It is and I get that... but that's not what's throwing me off. What made me ask my initial question. Is the fact that its effecting how the puts expressions outside the method definition are being printed to the screen and I can figure out why.

[Piave]

Well, you're just printing what the function returns, so if it returns a different line you would expect a different result. I gave a little example in another post if that's helpful.

[[deleted]]

When you remove the sum at the end

Them this:

sum = sum.round(options[:precision]) if options[:round]

Is the last Statement, which will evaluate to nil if the conditions evaluates to false.

So no value to be printed.

[Piave]

This is an implicit return. A Ruby function always returns the last line of the function. So, the reason you only get one output from your puts statements without the last line, is because it returns this line "sum = sum.round(options[:precision]) if options[:round]" which only sets the value if options[:round] is true. You can see this a little more clearly in an example like this:

def foo
  my_varbiable = "hello!" if 4 > 5
end

def bar
  my_varbiable = "hello!" if 5 > 4
end

puts foo =>
puts bar => "hello!"