Hidden features of Ruby

Continuing the "Hidden features of ..." meme, let's share the lesser-known but useful features of Ruby programming language.

Try to limit this discussion with core Ruby, without any Ruby on Rails stuff.

Solution 1:

From Ruby 1.9 Proc#=== is an alias to Proc#call, which means Proc objects can be used in case statements like so:

def multiple_of(factor)
  Proc.new{|product| product.modulo(factor).zero?}
end

case number
  when multiple_of(3)
    puts "Multiple of 3"
  when multiple_of(7)
    puts "Multiple of 7"
end

Solution 2:

Peter Cooper has a good list of Ruby tricks. Perhaps my favorite of his is allowing both single items and collections to be enumerated. (That is, treat a non-collection object as a collection containing just that object.) It looks like this:

[*items].each do |item|
  # ...
end

Solution 3:

Don't know how hidden this is, but I've found it useful when needing to make a Hash out of a one-dimensional array:

fruit = ["apple","red","banana","yellow"]
=> ["apple", "red", "banana", "yellow"]

Hash[*fruit]    
=> {"apple"=>"red", "banana"=>"yellow"}

Solution 4:

One trick I like is to use the splat (*) expander on objects other than Arrays. Here's an example on a regular expression match:

match, text, number = *"Something 981".match(/([A-z]*) ([0-9]*)/)

Other examples include:

a, b, c = *('A'..'Z')

Job = Struct.new(:name, :occupation)
tom = Job.new("Tom", "Developer")
name, occupation = *tom