Discovering Ruby object members?

Question

What is an easy way to find out what methods/properties that a ruby object exposes?

As an example to get member information for a string, in PowerShell, you can do

"" | get-member

In Python,

dir("")

Is there such an easy way to discover member information of a Ruby object?

score 75 · Accepted Answer · answered Jan 20 '11 at 12:30

75

"foo".methods

See:

http://ruby-doc.org/core/classes/Object.html

http://ruby-doc.org/core/classes/Class.html

http://ruby-doc.org/core/classes/Module.html

answered Jan 20 '11 at 12:30

noodl

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`"foo".methods - Object.methods` to be more specific – Roman Oct 18 '18 at 22:21

Andrew Grimm · Answer 2 · 2011-01-21T13:05:33.403

26

Ruby doesn't have properties. Every time you want to access an instance variable within another object, you have to use a method to access it.

edited Jan 21 '11 at 13:05

answered Jan 20 '11 at 22:14

Andrew Grimm

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It's great to know that everything is a method. Thanks Andrew – dance2die Jan 21 '11 at 12:57

score 17 · Answer 3 · answered Jan 20 '11 at 13:05

17

Two ways to get an object's methods:

my_object.methods
MyObjectClass.instance_methods

One thing I do to prune the list of inherited methods from the Object base class:

my_object.methods - Object.instance_methods

To list an object's attributes:

object.attributes

answered Jan 20 '11 at 13:05

Mark Thomas

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#attributes is AR specific; for a plain ruby object there's #instance_variables. Also, you can pass false as an argument to #methods to skip inherited ones. – noodl Jan 20 '11 at 13:07
@noodl, thanks. I meant instance_variables, but have too much Rails in my head :) – Mark Thomas Jan 20 '11 at 17:06
2

Kind of old, but `instance_variables` doesnt seem to show uninitialized variables, was hoping it showed attributes set with `attr_accessor` or its cousins – Karthik T Oct 17 '13 at 05:11

score 9 · Answer 4 · edited Nov 01 '16 at 16:20

There are two ways to accomplish this:

obj.class.instance_methods(false), where 'false' means that it won't include methods of the superclass, so for example having:

class Person
  attr_accessor :name
  def initialize(name)
    @name = name
  end
end

p1 = Person.new 'simon'
p1.class.instance_methods false # => [:name, :name=]
p1.send :name # => "simon"

the other one is with:

p1.instance_variables # => [:@name]
p1.instance_variable_get :@name # => "simon"

score 7 · Answer 5 · answered Dec 21 '15 at 15:53

7

Use this:

my_object.instance_variables

answered Dec 21 '15 at 15:53

Nimo

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score 2 · Answer 6 · answered Jan 20 '11 at 12:29

2

object.methods

will return an array of methods in object

answered Jan 20 '11 at 12:29

Arnaud Le Blanc

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Discovering Ruby object members?

6 Answers6