Ruby “.downcase! ” and “downcase” confusion

Question

I just started Ruby programming. I had read Difference Between downcase and downcase! in Ruby. However I encounter an interesting problem in practice, here is code:

Answer 1

a.downcase! modifies "a" directly -- you do not need to assign the result to "a".

1.9.3p362 :003 > a = "A"
 => "A" 
1.9.3p362 :004 > a.downcase!
 => "a" 
1.9.3p362 :005 > puts a
a
 => nil 
1.9.3p362 :006 > a = "A"
 => "A" 
1.9.3p362 :007 > a.downcase
 => "a" 
1.9.3p362 :008 > puts a
A
 => nil 

The danger of assigning variable = variable.downcase! is that if variable is already downcase then you have just set the variable to nil -- probably not your intent.

1.9.3p362 :001 > variable = 'a'                                                                                                                                                                                                                                               
 => "a"                                                                                                                                                                                                                                                                       
1.9.3p362 :002 > variable = variable.downcase!
 => nil                                                                                                                                                                                                                                                                       
1.9.3p362 :003 > puts variable                                                                                                                                                                                                                                                

 => nil