Question

If I define a top level method like this:

def inspect(x)
  # do something useful...
end

Then calling #inspect on a user-defined class stops working:

class Foo; end
p Foo.new # `inspect': wrong number of arguments (0 for 1) (ArgumentError)

However, it keeps working for classes like NilClass and String:

p nil    # prints 'nil'
p "test" # prints '"test"'

I thought that one explanation for this behaviour could be that top-level execution may be in the Object class itself, but it turns out that it’s in an instance of Object called main. Doesn’t this mean that methods defined here shouldn’t affect other classes?

Answer 1

main is a special place. Any methods defined there are defined as private instance methods of Object. This is so you can define pseudo-functions that can be called in any context without an explicit receiver.