Question

In the following program (written in irb shell) i call a method hidden of the class Tester that accepts 2 arguments both of them string and then returns a string after modifying them. I get an output which i don’t expect.

What i expect is:

def hidden(aStr,anotherStr) # After the call aStr = suhail and anotherStr = gupta
  anotherStr = aStr + " " + anotherStr
  # After the above statement anotherStr = suhail gupta
  return aStr + anotherStr.reverse 
  # After the above statement value returned should be suhailliahusatpug
  # i.e suhail + "reversed string of suhailgupta"
  end

  # But i get suhailatpug liahus

---

ACTUAL CODE:

1.9.3p194 :001 > class Tester
1.9.3p194 :002?>   def hidden(aStr,anotherStr)
1.9.3p194 :003?>     anotherStr = aStr + " " + anotherStr
1.9.3p194 :004?>     return aStr + anotherStr.reverse
1.9.3p194 :005?>     end
1.9.3p194 :006?>   end
1.9.3p194 :007 > o = Tester.new
=> #<Tester:0x9458b80> 
1.9.3p194 :008 > str1 = "suhail"
=> "suhail" 
1.9.3p194 :009 > str2 = "gupta"
=> "gupta" 
1.9.3p194 :010 > str3 = o.hidden(str1,str2)
=> "suhailatpug liahus" 

Why is that ? Is it a different matter in Ruby as compared to some other OOP language like Java ?

Answer 1

The Problem

You don’t have the string you think you do. Forget the method, just do it line-by-line:

# You passed these as parameters, so they're assigned.
aStr = 'suhail'
anotherStr = 'gupta'

# You re-assign a new string, including a space.
anotherStr = aStr + " " + anotherStr
=> "suhail gupta"

# You are concatenating two different strings.
aStr + anotherStr
=> "suhailsuhail gupta"

# You concatenate two strings, but are reversing only the second string.
aStr + anotherStr.reverse
=> "suhailatpug liahus"

This is all exactly as it should be.

The Solution

If you want “suhailatpugliahus” then you need to avoid reassigning a new value to anotherStr.

def hidden(aStr,anotherStr)
    aStr + (aStr + anotherStr).reverse
end  
hidden 'suhail', 'gupta'
=> "suhailatpugliahus"