Using Struct in Class Definition

Question

I have found very rare(to me) line of code in one of ours old repositories. Following code aws part of PoC application for simple Note taking app. Nevertheless, these two lines in model folder surprised me:

class Note < Struct.new(:title, :due_to, :body, :self_url, :image_url) 
end

I was looking up this technique for a while and haven't really found some valuable source of information about this implementaiton.

Can someone help me to better understand this? I think that this kind usage of Struct just creating new object which inherits from Struct. But I don't see the benefits here.

Alex Wayne · Accepted Answer · 2014-04-14 23:31:18Z

1

Struct.new(:title, :due_to, :body, :self_url, :image_url)
#=> #<Class:0x007fed5b1859c0>

Check that out, Struct.new returns a class. A class that can create instances with getters and setters for some named fields. And, of course, any class can be inherited from.

So this is simply a slightly odd way of defining a list of instance properties in the class declaration.

Which means this is funcationally the same as:

class Note
  attr_accessor :title, :due_to, :body, :self_url, :image_url
end

answered Apr 14, 2014 at 23:31

Alex Wayne

188k52 gold badges328 silver badges363 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Tom Hert Over a year ago

Ohh, thats seems to be pretty in fashion of DRY. Thank you for your answer. Is this common? Is there any limitations in using this?

Alex Wayne Over a year ago

It's a little obtuse. If you came across the functionally equivalent version that I posted at the end of my answer, would you have come here to ask this question? Probably not, because it would have been obvious.

Tom Hert Over a year ago

Yeah, you're right. Thank you for clarification. I already tested it.

Chuck Over a year ago

The class Note; attr_accessor… version isn't quite equivalent. It doesn't get the hashlike behavior of a Struct.

Chuck · Accepted Answer · 2014-04-15 00:05:45Z

0

That line of code is an idiosyncratic way of declaring a Struct-based class. The more normal way of doing it is (in my experience):

Note = Struct.new(:title, :due_to, :body, :self_url, :image_url) do
  …
end

Struct classes get automatic accessors and an initialize method for their named attributes, as well as a Hash-like interface that includes [] and []= for getting and setting the named attributes, each_pair for the attributes and a few other goodies. Structs are very nice for POD-ish types.

answered Apr 15, 2014 at 0:05

Chuck

238k31 gold badges306 silver badges392 bronze badges

Collectives™ on Stack Overflow

Using Struct in Class Definition

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related