assignment gotchas

assignment_gotchas.rb

@counter = 0

def big_calculation
  @counter += 1
end
private :big_calculation

heading "before local variable assignment, with implicit receiver"
item "big_calculation"
puts big_calculation
item "big_calculation"
puts big_calculation
item "big_calculation"
puts big_calculation

big_calculation = big_calculation
heading "after local variable assignment"
item "big_calculation"
puts big_calculation.inspect
item "big_calculation"
puts big_calculation.inspect
item "big_calculation"
puts big_calculation.inspect

heading "explicit receiver"
item "self.big_calculation"
begin
  self.big_calculation
rescue => e
  puts "exception caught:"
  puts e.message, e.backtrace
end

heading "implicit receiver"
item "big_calculation()"
puts big_calculation()
item "big_calculation()"
puts big_calculation()
item "big_calculation()"
puts big_calculation()


# helpers
BEGIN {
  DATA.instance_eval { truncate pos.tap { reopen __FILE__, "a+" } }
  $stdout = DATA

  def heading str
    print "\n\n-----> #{str}\n"
  end

  def item str
    print "> #{str}\n#=> "
  end
}
__END__


-----> before local variable assignment, with implicit receiver
> big_calculation
#=> 1
> big_calculation
#=> 2
> big_calculation
#=> 3


-----> after local variable assignment
> big_calculation
#=> nil
> big_calculation
#=> nil
> big_calculation
#=> nil


-----> explicit receiver
> self.big_calculation
#=> exception caught:
private method `big_calculation' called for main:Object
assignment.rb:28:in `<main>'


-----> implicit receiver
> big_calculation()
#=> 4
> big_calculation()
#=> 5
> big_calculation()
#=> 6