Ruby: String to String comparison failed (ArgumentError)

Make sure you return the comparison result from the block you passed to sort!

.

You are currently returning nil

(the return value of the last operator, puts

), which leads to unpredictable results.

Change your code to:

books = ["Charlie and the Chocolate Factory", "War and Peace", "Utopia", "A Brief History of Time", "A Wrinkle in Time"]

books.sort! {

  |firstBook, secondBook|
  boolean_value = firstBook <=> secondBook
  print "first book is =  '#{firstBook}'"
  print " , second book is = '#{secondBook}'"
  puts  " and there compare result is #{boolean_value}"

  boolean_value  # <--- this line has been added
}

      

        
        
        
      

    

and everything will work.

Offtopic, multiple nitpicks:

• in Ruby, the convention is to separate underscore words in variable names. For example, you should rename firstBook
  
  →first_book
  
  
• you must be very careful when renaming variables. The variable boolean_value
  
  here is a little misleading because it is not true
  
  either false
  
  , her -1
  
  , 0
  
  or 1
  
  .