Extraordinarily Simple Ruby Question: Where's My Class?

Question

[I'm just starting with Ruby, but "no question is ever too newbie," so I trudge onwards...]

Every tutorial and book I see goes from Ruby with the interactive shell to Ruby on Rails. I'm not doing Rails (yet), but I don't want to use the interactive shell. I have a class file (first_class.rb) and a Main (main.rb). If I run the main.rb, I of course get the uninitialized constant FirstClass. How do I tell ruby about the first_class.rb?

Answer 1

The easiest way is to put them both in the same file.

However you can also use require, e.g.:

require 'first_class'

Answer 2

You can also use autoload as follows:

autoload :FirstClass, 'first_class'

This code will automatically load first_class.rb as soon as FirstClass is used. Note, however, that the current implementations of autoload are not thread safe (see http://www.ruby-forum.com/topic/174036).

Answer 3

There's another point worth noting: you wouldn't typically use a main file in ruby. If you're writing a command line tool, standard practice would be to place the tool in a bin subdirectory. For normal one-off scripts the main idiom is:

if __FILE__ == $0
  # main does here
  # `__FILE__` contains the name of the file the statement is contained in
  # `$0` contains the name of the script called by the interpreter
  # 
  # if the file was `required`, i.e. is being used as a library
  # the code isn't executed.
  # if the file is being passed as an argument to the interpreter, it is.
end