# What is \[\] here **URL:** \ **Category:** Ruby\ **Created:** [October 16, 2008, 3:59pm UTC](https://www.ruby-forum.com/t/what-is-here/151080 "2008-10-16T15:59:13Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![dorelal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3da27b/32.png) [@dorelal](https://www.ruby-forum.com/u/dorelal)\ **Post date:** [October 16, 2008, 3:59pm UTC](https://www.ruby-forum.com/t/what-is-here/151080/1 "2008-10-16T15:59:13Z")
class User puts [].methods.size puts self.methods.size end What does it mean to have [] method at a class level? Where is the documentation for it? ---
**Author:** ![dorelal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3da27b/32.png) [@dorelal](https://www.ruby-forum.com/u/dorelal)\ **Post date:** [October 16, 2008, 4:09pm UTC](https://www.ruby-forum.com/t/what-is-here/151080/2 "2008-10-16T16:09:12Z")
On Oct 16, 2008, at 8:58 AM, Raj S. wrote: > class User > puts [].methods.size > puts self.methods.size > end > > What does it mean to have [] method at a class level? Where is the > documentation for it? [] here is the empty array, not a method call. So [].methods.size just returns how many methods are defined for an instance of Array. Why it’s at class level, I’ve no idea. There doesn’t seem to be any need to have it there. ---
**Author:** ![dorelal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3da27b/32.png) [@dorelal](https://www.ruby-forum.com/u/dorelal)\ **Post date:** [October 16, 2008, 4:10pm UTC](https://www.ruby-forum.com/t/what-is-here/151080/3 "2008-10-16T16:10:23Z")
class User > puts [].methods.size > puts self.methods.size > end > > What does it mean to have [] method at a class level? Where is the > documentation for it? Here, [] is just an empty array literal. [].methods.size returns the number of public methods that an array has. ---
**Author:** ![dorelal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3da27b/32.png) [@dorelal](https://www.ruby-forum.com/u/dorelal)\ **Post date:** [October 16, 2008, 4:15pm UTC](https://www.ruby-forum.com/t/what-is-here/151080/4 "2008-10-16T16:15:17Z")
I should have mentioned that I picked up the code from the source code of named\_scope.rb ( from rails). In rails the code is [].methods.each do |m| unless m =~ /(^\_\_|^nil?|^send|^object\_id$|class|extend|^find$|count|sum|average|maximum|minimum|paginate|first|last|empty?|respond\_to?)/ delegate m, :to =\> :proxy\_found end end [].methods was throwing me off. ---
**Author:** ![dorelal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3da27b/32.png) [@dorelal](https://www.ruby-forum.com/u/dorelal)\ **Post date:** [October 16, 2008, 4:16pm UTC](https://www.ruby-forum.com/t/what-is-here/151080/5 "2008-10-16T16:16:51Z")
On Thu, Oct 16, 2008 at 3:58 PM, Raj S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > class User > puts [].methods.size > puts self.methods.size > end > > What does it mean to have [] method at a class level? Where is the > documentation for it? [] is a literal for a new empty Array. irb(main):001:0\> [].object\_id =\> -606116168 irb(main):002:0\> [].object\_id =\> -606126028 irb(main):003:0\> [].object\_id =\> -606134558 irb(main):004:0\> [].class =\> Array Jesus. ---
**Author:** ![dorelal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3da27b/32.png) [@dorelal](https://www.ruby-forum.com/u/dorelal)\ **Post date:** [October 16, 2008, 4:14pm UTC](https://www.ruby-forum.com/t/what-is-here/151080/6 "2008-10-16T16:14:30Z")
2008/10/16 Raj S. \: > What does it mean to have [] method at a class level? Where is the > documentation for it? It is the empty array. Just type [].class =\> Array [].size =\> 0 Regards, Serabe ---
**Author:** ![dorelal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3da27b/32.png) [@dorelal](https://www.ruby-forum.com/u/dorelal)\ **Post date:** [October 16, 2008, 5:06pm UTC](https://www.ruby-forum.com/t/what-is-here/151080/7 "2008-10-16T17:06:19Z")
[] is a way to declare an empty array. It’s a nice alternative to Array.new. puts [].methods.size will print the number of methods on a new, empty Array instance. On my Ruby install (1.8.6 p114 on Mac OS X 10.5.5), the output is 121. Craig ---
**Author:** ![dorelal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3da27b/32.png) [@dorelal](https://www.ruby-forum.com/u/dorelal)\ **Post date:** [October 16, 2008, 5:15pm UTC](https://www.ruby-forum.com/t/what-is-here/151080/8 "2008-10-16T17:15:08Z")
On 16.10.2008 16:13, Serabe wrote: > 2008/10/16 Raj S. \: > > > What does it mean to have [] method at a class level? Where is the > > documentation for it? > > It is the empty array. Just type > > [].class =\> Array > [].size =\> 0 It is not _the_ empty Array but _an_ empty Array. Things like [], “” and ‘’ are actually constructors for new objects. This is important to keep in mind. Especially people coming from Java might get the wrong impression, that a = “foo” b = “foo” will create two variables pointing to the same object. In reality, there are two variables pointing to two different objects. You can easily see that from $ ruby -e ‘4.times do p [[],"",’’’’].map {|o|o.object\_id} end’ [134314000, 134313990, 134313980] [134313890, 134313880, 134313870] [134313790, 134313780, 134313770] [134313690, 134313680, 134313670] Kind regards robert ---
**Author:** ![dorelal](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3da27b/32.png) [@dorelal](https://www.ruby-forum.com/u/dorelal)\ **Post date:** [October 16, 2008, 5:23pm UTC](https://www.ruby-forum.com/t/what-is-here/151080/9 "2008-10-16T17:23:57Z")
> puts [].methods.size A more explicit alternative is puts Array.instance\_methods.size – Mark.