Question

I am just getting started with Ruby on Rails. Coming from the Java world, one thing that I am wondering is how do Ruby/Rails developers find out where methods are actually defined.

I am used to just clicking on the method in Eclipse to find where is is defined even in third party libraries (supposing I have the source code).

A concrete example: I am trying to find out how the Authlogic gem apparently changes the constructor of my User class to require an additional parameter (called :password_confirmation) even though the User class doesn’t even inherit from anything related to Authlogic.

Probably I am just overlooking something really obvious here (or maybe I still can’t wrap my head around the whole “convention over configuration” thing ;-))

Answer 1

The Pry gem is designed precisely for this kind of explorative use-case.

Pry is an interactive shell that lets you navigate your way around a program’s source-code using shell-like commands such as cd and ls.

You can pull the documentation for any method you encounter and even view the source code, including the native C code in some cases (with the pry-doc plugin). You can even jump directly to the file/line where a particular method is defined with the edit-method command. The show-method and show-doc commands also display the precise location of the method they’re acting on.

Watch the railscast screencast for more information.

Here are some examples below:

pry(main)> show-doc OpenStruct#initialize

From: /Users/john/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/ostruct.rb @ line 46:
Number of lines: 11

visibility:  private
signature:  initialize(hash=?)

Create a new OpenStruct object.  The optional hash, if given, will
generate attributes and values.  For example.

  require 'ostruct'
  hash = { "country" => "Australia", :population => 20_000_000 }
  data = OpenStruct.new(hash)

  p data        # -> <OpenStruct country="Australia" population=20000000>

By default, the resulting OpenStruct object will have no attributes.

pry(main)> 

You can also look up sourcecode with the show-method command:

pry(main)> show-method OpenStruct#initialize

From: /Users/john/.rvm/rubies/ruby-1.9.2-p180/lib/ruby/1.9.1/ostruct.rb @ line 46:
Number of lines: 9

def initialize(hash=nil)
  @table = {}
  if hash
    for k,v in hash
      @table[k.to_sym] = v
      new_ostruct_member(k)
    end
  end
end
pry(main)> 

See http://pry.github.com for more information 🙂