Question

I have seen here and there code like this one

Specification.new do |s|
  s.name = %q{casein}
  s.version = "3.1.11"
....

Can someone explain me what is the idea behind “do |s|” ?

Answer 1

This is an example of using blocks in ruby. Block is a chunk of code that you can pass to a method (new is just a regular method).

class Foo
  def initialize
    puts "doing some work"
    yield('Foo') if block_given?
  end
end

Foo.new do |s|
  puts "output from #{s}"
end
# >> doing some work
# >> output from Foo

Here initializer in Foo calles a block (if one is given) and passes it a parameters. Block then can receive that parameter and do its work.

Educational reading here.