Challenge 2: require vs require_relative — Solution

# lib/greeting.rb
module Greeting
  def self.hello(name)
    "Hello, #{name}!"
  end
end

# main.rb
require_relative "lib/greeting"

puts Greeting.hello("Philip")

# Why require (not require_relative) would be wrong here:
# require resolves against Ruby's load path (gems and the standard
# library), NOT relative to the current file's location. If main.rb used
# require "lib/greeting" instead, it would only work by accident, and
# only if the program happened to be run from the exact directory
# containing main.rb -- run it from anywhere else, or move main.rb into a
# subfolder, and require "lib/greeting" would fail to find the file at
# all. require_relative always resolves relative to greeting.rb's actual
# location on disk, regardless of the current working directory the
# program was launched from, which is exactly the guarantee a local
# project file needs.

=begin
Notes:
- Greeting is a module (not a class) since hello is meant to be called
  directly on Greeting itself, similar to a static/utility method in PHP
  or Python, not as an instance method on individual objects.
- require_relative "lib/greeting" in main.rb resolves relative to main.rb
  itself, so this works correctly no matter what directory the ruby
  main.rb command is actually run from.
- The .rb extension is optional in both require and require_relative --
  "lib/greeting" and "lib/greeting.rb" both resolve to the same file.
=end