I read this:
Let’s start with a simple Ruby program. We’ll write a method that returns a cheery, personalized greeting.
def say_goodnight(name) result = "Goodnight, " + name return result end
My understanding is that a method is a function or subroutine that is defined in a class, which can be associated to a class (class method) or to an object (instance method).
Then, how can that be a method if it was not defined within a class?
When you define a function in Ruby at the global scope in this way, it technically becomes a private method of the Object class, which is the base class that everything inherits from in Ruby. Everything in Ruby is an object, so it is indeed true that you have defined a method.
def say_goodnight(name)
result = "Goodnight, " + name
return result
end
Object.private_methods.include? :say_goodnight
=> true
Because it is defined as a method with private visibility on Object, it can only be called inside objects of the class on which it's defined or subclasses. So why does it appear to be available globally?
Basically, the Ruby program itself defines an instance of Object called main, which serves as the top-level scope where your method was defined. So if you think of your program as running inside main (which is an Object) its private methods are available for use.
# In irb:
self
=> main
self.class
=> Object
self.private_methods.include? :say_goodnight
=> true
Addendum:
This answer which further explains how main is defined and implemented.
Noted in the comment thread, later versions of Ruby would define the method Object#say_goodnight in this example with public visibility rather than private. This behavior appears to have changed between Ruby 2.2.x and 2.3.x, but does not affect method exposure.
