CODEWITHSUNDEEP
rubytypes
Zippy Zeppoli
Zippy Zeppoli

Reputation: 6077

Determining type of an object in ruby

I'll use python as an example of what I'm looking for (you can think of it as pseudocode if you don't know Python):

>>> a = 1
>>> type(a)
<type 'int'>

I know in ruby I can do :

1.9.3p194 :002 > 1.class
 => Fixnum

But is this the proper way to determine the type of the object?

Upvotes: 489

Views: 723462

Answers (6)

Douglas G. Allen
Douglas G. Allen

Reputation: 2261

I would say "yes". Matz had said something like this in one of his talks, "Ruby objects have no types." Not all of it but the part that he is trying to get across to us. Why would anyone have said "Everything is an Object" then? To add he said "Data has Types not objects".

RubyConf 2016 - Opening Keynote by Yukihiro 'Matz' Matsumoto

But Ruby doesn't care as much about the type of object as the class. We use classes, not types. All data, then, has a class.

12345.class

'my string'.class

Classes may also have ancestors

Object.ancestors

They also have meta classes but I'll save you the details on that.

Once you know the class then you'll be able to lookup what methods you may use for it. That's where the "data type" is needed. If you really want to get into details the look up...

"The Ruby Object Model"

This is the term used for how Ruby handles objects. It's all internal so you don't really see much of this but it's nice to know. But that's another topic.

Yes! The class is the data type. Objects have classes and data has types. So if you know about data bases then you know there are only a finite set of types.

text blocks numbers

Upvotes: 38

shakib
shakib

Reputation: 101

every variable have a prop with name class. if you print it, it will tell you what type it is. so do like this:

puts a.class

Upvotes: 6

Fazal Ur Rehman Fazal
Fazal Ur Rehman Fazal

Reputation: 129

variable_name.class

Here variable name is "a" a.class

Upvotes: 5

tadman
tadman

Reputation: 211560

The proper way to determine the "type" of an object, which is a wobbly term in the Ruby world, is to call object.class.

Since classes can inherit from other classes, if you want to determine if an object is "of a particular type" you might call object.is_a?(ClassName) to see if object is of type ClassName or derived from it.

Normally type checking is not done in Ruby, but instead objects are assessed based on their ability to respond to particular methods, commonly called "Duck typing". In other words, if it responds to the methods you want, there's no reason to be particular about the type.

For example, object.is_a?(String) is too rigid since another class might implement methods that convert it into a string, or make it behave identically to how String behaves. object.respond_to?(:to_s) would be a better way to test that the object in question does what you want.

Upvotes: 763

Arup Rakshit
Arup Rakshit

Reputation: 118261

you could also try: instance_of?

p 1.instance_of? Fixnum    #=> True
p "1".instance_of? String  #=> True
p [1,2].instance_of? Array #=> True

Upvotes: 111

Stuart M
Stuart M

Reputation: 11588

Oftentimes in Ruby, you don't actually care what the object's class is, per se, you just care that it responds to a certain method. This is known as Duck Typing and you'll see it in all sorts of Ruby codebases.

So in many (if not most) cases, its best to use Duck Typing using #respond_to?(method):

object.respond_to?(:to_i)

Upvotes: 53

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