Ruby expression evaluation: whitespace matters?

Question

Imagine it's Jan 19. This will not be hard if you look at this question today.

Date.today
 => Thu, 19 Jan 2012    # as expected

Date.today + 1
 => Fri, 20 Jan 2012    # as expected

Date.today+1
 => Fri, 20 Jan 2012    # as expected

Date.today +1
 => Thu, 19 Jan 2012    # ?!

What am I missing here?

Answer 1

The difference is that:

Date.today + 1 

is an addition of two numerical values and

Date.today +1 

is a call to the method today with the parameter sg(day of calendar reform) with value +1

The best way to examine this is to monkey patch the original method with debug output included. See this script as example:

require 'date'

class Date

  def self.today(sg=ITALY)
     puts "ITALY default("+sg.to_s+")" if sg==ITALY
     puts sg unless sg==ITALY
     jd = civil_to_jd(*(Time.now.to_a[3..5].reverse << sg))
     new0(jd_to_ajd(jd, 0, 0), 0, sg)
  end

end

puts "- Addition:"
Date.today + 1
puts "- Parameter:"
Date.today +1

This will print the following console output:

- Addition:
ITALY default(2299161)
- Parameter:
1