private_methods.rb

class Foo
  def initialize
    @foo = :foo
  end
  
  private
  
  def bar
    :bar
  end
end

f = Foo.new
f.bar #=> NoMethodError private method

class Foo
  def public_bar
    bar
  end
end

f.public_bar #=> :bar

class Foo
  def public_bar
    self.bar
  end
end

f.public_bar #=> NoMethodError private method

# OK, fair enough, private methods cannot be called with receivers (i.e. self.bar)

# But...

class Foo
  private
  
  def bar=(val)
    @barf = val
  end
end

f.bar = 42 #=> NoMethodError private method

# OK, fair enough

# But...

class Foo
  def public_bar
    self.bar = 99
  end
end

f.public_bar #=> 99
f #=> #<Foo:0x0000564c337d45f8 @foo=:foo, @barf=99>

# So, if Foo#bar= is a private method, how come Foo#public_bar can call it on self?