I recently encountered some methods I didn't know about.

~

The tilde method (~) is used by Sequel and you can use it like this:

class Post
  def ~
    11
  end
end

post = Post.new
~post # => 11

That's right: you call this method by placing the tilde before the object.

In Sequel it is used to perform NOT queries, by defining the tilde on Symbol:

Post.where(~:deleted_at => nil)
# => SELECT * FROM posts WHERE deleted_at IS NOT NULL

-@

The minus-at (-@) method works just about the same as the tilde method. It is the method called when a minus-sign is placed before the object. In effect, this means that Fixnum is implemented somewhere along the lines of this:

class Fixnum
  def -@
    self * -1
  end
end

num = 10
negative = -num # => -10

I found this one browsing through the source of the ActiveSupport::Duration class (you know, the one you get when you do 1.day). I guess it makes sense.

Be careful with chaining methods though:

ruby-1.9.1-p378 > num = 5
 => 5
ruby-1.9.1-p378 > -num.to_s
NoMethodError: undefined method `-@' for "5":String
  from (irb):5
  from /Users/iain/.rvm/rubies/ruby-1.9.1-p378/bin/irb:17:in `<main>'

This also applies to the tilde method.

So?

I don't know. Enrich your DSLs and APIs, if it makes any sense to do it.