How to list all methods for an object in Ruby?

Question

How do I list all the methods that a particular object has access to?

I have a @current_user object, defined in the application controller:

def current_user
  @current_user ||= User.find(session[:user_id]) if session[:user_id]
end

And want to see what methods I have available to me in the view file. Specifically, I want to see what methods a :has_many association provides. (I know what :has_many should provide, but want to check that.)

Answer 1

The following will list the methods that the User class has that the base Object class does not have...

>> User.methods - Object.methods
=> ["field_types", "maximum", "create!", "active_connections", "to_dropdown",
    "content_columns", "su_pw?", "default_timezone", "encode_quoted_value", 
    "reloadable?", "update", "reset_sequence_name", "default_timezone=", 
    "validate_find_options", "find_on_conditions_without_deprecation", 
    "validates_size_of", "execute_simple_calculation", "attr_protected", 
    "reflections", "table_name_prefix", ...

Note that methods is a method for Classes and for Class instances.

Here's the methods that my User class has that are not in the ActiveRecord base class:

>> User.methods - ActiveRecord::Base.methods
=> ["field_types", "su_pw?", "set_login_attr", "create_user_and_conf_user", 
    "original_table_name", "field_type", "authenticate", "set_default_order",
    "id_name?", "id_name_column", "original_locking_column", "default_order",
    "subclass_associations",  ... 
# I ran the statements in the console.

Note that the methods created as a result of the (many) has_many relationships defined in the User class are not in the results of the methods call.

Added Note that :has_many does not add methods directly. Instead, the ActiveRecord machinery uses the Ruby method_missing and responds_to techniques to handle method calls on the fly. As a result, the methods are not listed in the methods method result.

Answer 2

Or just User.methods(false) to return only the methods defined within that class.

Answer 3

Module#instance_methods

Returns an array containing the names of the public and protected instance methods in the receiver. For a module, these are the public and protected methods; for a class, they are the instance (not singleton) methods. With no argument, or with an argument that is false, the instance methods in mod are returned, otherwise the methods in mod and mod’s superclasses are returned.

module A
  def method1()  end
end
class B
  def method2()  end
end
class C < B
  def method3()  end
end

A.instance_methods                #=> [:method1]
B.instance_methods(false)         #=> [:method2]
C.instance_methods(false)         #=> [:method3]
C.instance_methods(true).length   #=> 43

Answer 4

You can do

current_user.methods

For better listing

puts "\n\current_user.methods : "+ current_user.methods.sort.join("\n").to_s+"\n\n"

Answer 5

What about one of these?

object.methods.sort
Class.methods.sort

Answer 6

If You are looking list of methods which respond by an instance (in your case @current_user). According to ruby documentation methods

Returns a list of the names of public and protected methods of obj. This will include all the methods accessible in obj's ancestors. If the optional parameter is false, it returns an array of obj's public and protected singleton methods, the array will not include methods in modules included in obj.

@current_user.methods
@current_user.methods(false) #only public and protected singleton methods and also array will not include methods in modules included in @current_user class or parent of it.

Alternatively, You can also check that a method is callable on an object or not?.

@current_user.respond_to?:your_method_name

If you don't want parent class methods then just subtract the parent class methods from it.

@current_user.methods - @current_user.class.superclass.new.methods #methods that are available to @current_user instance.

Answer 7

Suppose User has_many Posts:

u = User.first
u.posts.methods
u.posts.methods - Object.methods

Answer 8

To expound upon @clyfe's answer. You can get a list of your instance methods using the following code (assuming that you have an Object Class named "Parser"):

Parser.new.methods - Object.new.methods