From: Justin Collins <justincollins@...>
Date: 2013-06-28T14:56:49+09:00
Subject: Re: Where's this ruby feature documented? ...and the case of an accidentally discovered feature.

On 06/27/2013 04:24 PM, Kendall Gifford wrote:
> So, while doing some random testing in an IRB session, I accidentally
> discovered a feature of ruby that is new to me. Apparently, you can call
> a method named "call" by omitting the name of the method you wish to call:
>
> 1.9.3-p194 :001 > x = -> { puts "Hello, world." }
>   => #<Proc:0x007f820d179710@(irb):1 (lambda)>
> 1.9.3-p194 :002 > x.()
> Hello, world.
>   => nil
>
> Or, more explicitly:
>
> 1.9.3-p194 :001 > class X
> 1.9.3-p194 :002?>   def call(name)
> 1.9.3-p194 :003?>     puts "Hello, #{name}"
> 1.9.3-p194 :004?>     end
> 1.9.3-p194 :005?>   end
>   => nil
> 1.9.3-p194 :006 > x = X.new
>   => #<X:0x007f968b92e6d0>
> 1.9.3-p194 :007 > x.("Bob")
> Hello, Bob
>   => nil
>
> In all the books, articles, blogs, and tutorials that I've read, I don't
> recall any every mentioning this feature anywhere. As soon as I stumbled
> on this feature, I search the Pickaxe book and Google to see if and
> where this feature was documented. No luck.
>
> What I did end up finding was a chunk of example code from the jbuilder
> gem's README that uses this feature:
> https://github.com/rails/jbuilder/blob/master/README.md
>
> Specifically, the 3rd line in the first code example:
>
> json.(@message, :created_at, :updated_at)
>
> I'm sure there's code and examples out there that also use this feature.
> However, what I'd really be interested in knowing is just what this
> feature is officially called and where it's documented (I'm just really
> OCD and curious about some things).
>
> Anyone know of the top your head? How long has this feature been in
> ruby? All along? Is it a newer feature?

It was added in Ruby 1.9. It is mentioned somewhat in passing in the 
docs for Proc#call: 
http://www.ruby-doc.org/core-1.9.3/Proc.html#method-i-call

 From what I can tell, this syntax just isn't that popular. I have 
definitely never seen it used as a proxy for #call on an object other 
than a Proc, although I admit it's kind of cool.

-Justin