What is the %w "thing" in ruby?

Question

I'm referring to the %w operator/constructor/whatever you may call it, used like this:

%w{ foo bar baz }
=> ["foo", "bar", "baz"]

I have several questions about it:

• What is the proper name of that %w "thing"? Operator? Literal? Constructor?
• Does it matter whether I use {}s instead of []s?
• Are there any other things like this (for example, one that gives you an array of symbols instead)?
• Can they be nested (one %w inside another %w, in order to create nested arrays)?
• Where can I find documentation about it?

Answer 1

1) It is a litteral, where it is a % then a r(regular expression), w(array), q(string) etc to denote different litterals.

2)

ruby-1.9.2-p136 :001 > %w{1 2 3}
 => ["1", "2", "3"] 
ruby-1.9.2-p136 :002 > %w[1 2 3]
 => ["1", "2", "3"] 

ruby-1.9.2-p136 :008 > %w!a s d f!
 => ["a", "s", "d", "f"] 

ruby-1.9.2-p136 :009 > %w@a s d f@
 => ["a", "s", "d", "f"] 

So you can see that you can use any charater as long as it marks both the beginning and end of the content.

3)

Here are some other examples:

Strings:(%q or %Q)

ruby-1.9.2-p136 :016 > %Q[ruby is cool]
 => "ruby is cool" 
ruby-1.9.2-p136 :017 > %q[ruby is "cool"]
 => "ruby is \"cool\"" 

Regex: (%r)

ruby-1.9.2-p136 :019 > %r[(\w+)]
 => /(\w+)/ 

Sys command: (%x)

ruby-1.9.2-p136 :020 > %x[date]
 => "Tue Mar 29 12:55:30 EDT 2011\n"

4) They cannot be nested because the %w means white space divided array. So if you try to do multi level, it would look like this:

ruby-1.9.2-p136 :003 > %w{1 %w{2 3 4} 5}
 => ["1", "%w{2", "3", "4}", "5"] 

To accomplish this, you would need to use the more verbose syntax:

ruby-1.9.2-p136 :011 > [1, [2,3,4], 5]
 => [1, [2, 3, 4], 5]