Comments on: Understanding Ruby and Rails: Delegate

By: Yan Cherfan

Yan Cherfan — Sun, 04 Dec 2011 16:07:06 +0000

Very useful post. Thanks!

By: bra1n

bra1n — Tue, 20 Sep 2011 10:51:13 +0000

def ma,e
# let’s use try to bypass nil-check
user.try(:name)
end

seems like a typo, too…? Or did you indeed mean “ma,e” instead of “name”?

By: Simone Carletti

Simone Carletti — Thu, 11 Aug 2011 20:45:01 +0000

You’re right, there’s a typo. To keep it simple, I changed the first example to assume the method to be invoked is called author.
Thanks for pointing it out. :)

By: fearless fool

fearless fool — Thu, 11 Aug 2011 20:13:39 +0000

I’m a little late to the party, but I don’t understand how the first example of delegation works:

class Post
belongs_to :user
delegate :author, :to => :user, :allow_nil => true
end

Either there’s a typo, or User magically knows that :author really means to invoke the :name method, or I’m missing something fundamental. I’m hoping its the former. Clarification?

By: rubyu2

rubyu2 — Sat, 09 Oct 2010 08:37:17 +0000

i agree that the ‘post.new.user.name’ style.
but sometime i will write a method like that ‘def user_name self.user.name end’ if use user_name offen.

By: A Rubyist’s Beautiful Mistress: method_missing - Alfa Jango Blog

A Rubyist’s Beautiful Mistress: method_missing - Alfa Jango Blog — Fri, 08 Oct 2010 20:10:59 +0000

[...] you take what you can get. If you want more readable code, check out ruby delegation library and Rails ActiveRecord delegation. So, let’s put this all together to see the real power of define_method. This is adapted [...]

By: Glenn R

Glenn R — Tue, 01 Jun 2010 08:40:47 +0000

Hi Kally

I agree that the ‘Post.new.user.name’ style of doing things can be more natural and readable, but it may be a sign of coupling in your app.

There’s a good discussion of it here: http://haacked.com/archive/2009/07/14/law-of-demeter-dot-counting.aspx

I try to always keep in mind that those long chained method calls are a bit of a code smell, and to consider a refactor with delegate() if it makes sense.

By: Understanding Ruby and Rails: Proxy Patter, Dynamic Delegation and BasicObject – Simone Carletti's Blog

Thu, 13 May 2010 07:57:47 +0000

[...] For the most part of Ruby code, this change won’t mean anything special. However the BasicObject plays a fundamental role to implement the proxy pattern and dynamic delegation. [...]

By: Kally

Kally — Tue, 12 Jan 2010 16:10:54 +0000

I’m probably wrong, but I feel like this is more useful with non-activerecord classes, although most people think the exact opposite.
For example, if I want to write
Post.new.user_name, it makes more sense to me to write Post.new.user.name, same number of characters, but it is more clear what’s happening, without any quasi-virtual attribute.
Interesting anyway the technique in general.
Thanks.

By: brainopia

brainopia — Tue, 15 Dec 2009 20:38:07 +0000

Don’t forget to mention forwardable.