block, proc and &

call method with block parameter:

two syntaxes:

1.  {   } 

     this is useful for one line

2. do   end

    this is useful for multiple line

ex:

["a", "b"].each do |i|

    puts "#{i}"

end

the element between |  | refers to each element in the array  

define a method with block parameter

use &

ex:

class Array

     def test( &arg)

           find_all( &arg)

     end    

end

pass proc parameter to a method received block

ex:

a=lambda{ puts "abc"}

test(&a)