Loading help documentation alters irb results - ruby

Question

I'm learning Ruby, and went into irb to test something out with the Date class. In short, I did the following:
$ irb
irb(main):001:0> Date.new
=> #<Date:0x007f983103ee60>
irb(main):002:0> Date.constants
=> []
irb(main):003:0> help Date
=> nil
irb(main):004:0> Date.constants
=> [:MONTHNAMES, :ABBR_MONTHNAMES, :DAYNAMES, :ABBR_DAYNAMES, :ITALY, :ENGLAND, :JULIAN, :GREGORIAN, :Infinity]
irb(main):005:0>
I'm so confused by this. Questions:
Why would reading help documentation cause the output of Date.constants to change?
Presumably help is loading/initializing something. What is it? And why did Date.new work?
Is whatever this is something I need to worry about when writing .rb files?
This is tough to Google for. I'm on ruby 2.1.2 and irb 0.9.6.

Answer 1

The most likely cause of the addition of the Date constants after running help Date is that somewhere in the execution of the command, require 'date' (or require 'time') is called:
2.1.0 :001 > Date.constants
=> []
2.1.0 :002 > require 'date'
=> true
2.1.0 :003 > Date.constants
=> [:MONTHNAMES, :ABBR_MONTHNAMES, :DAYNAMES, :ABBR_DAYNAMES, :ITALY, :ENGLAND, :JULIAN, :GREGORIAN, :Infinity]
As for Date.new, it works because Date comes with a default constructor.
I doubt this will ever be problematic for you.