alexblom · December 11, 2015 07:59 · Jan 19, 2013 · Jan 19, 2013 · Jan 19, 2013
diff --git a/string_concatenation.rb b/string_concatenation.rb
@@ -66,4 +66,16 @@
 
 #Full name will still be a *ptr to first_name
 1.9.3p125 :023 > full_name.object_id
- => 70105706563920 
+ => 70105706563920 
+
+#Thus, be wary of assignment pre concat
+1.9.3p125 :024 > first_name = "Alex"
+ => "Alex" 
+1.9.3p125 :025 > full_name = ""
+ => "" 
+1.9.3p125 :026 > full_name << first_name
+ => "Alex" 
+1.9.3p125 :027 > full_name << last_name
+ => "Alex Blom" 
+1.9.3p125 :028 > first_name
+ => "Alex" 
diff --git a/string_concatenation.rb b/string_concatenation.rb
@@ -40,7 +40,7 @@
 1.9.3p125 :013 > full_name.concat(last_name)
  => "Alex Blom" 
 
-#Because the pointer was not broken, first_name has the expected value of full_name
+#Because the pointer was not broken, first_name has the unexpected value of full_name
 1.9.3p125 :014 > first_name
  => "Alex Blom" 
 

diff --git a/string_concatenation.rb b/string_concatenation.rb
@@ -0,0 +1,69 @@
+# When assigning string a = string b, Ruby simply makes string b a *ptr to string a
+# The generic string a += string b will convert string b to a new object
+# String concatenation (a.concat(b), a << b) will not, leading to unexpected values for a
+
+#Initialize first and last name
+1.9.3p125 :002 > first_name = "Alex"
+ => "Alex" 
+1.9.3p125 :003 > last_name = " Blom"
+ => " Blom" 
+
+#Join strings with +  
+1.9.3p125 :004 >   full_name = first_name
+ => "Alex" 
+1.9.3p125 :005 > full_name += last_name
+ => "Alex Blom" 
+
+#Confirm variables are as we would expect
+1.9.3p125 :006 > first_name
+ => "Alex" 
+1.9.3p125 :007 > last_name
+ => " Blom" 
+1.9.3p125 :008 > full_name
+ => "Alex Blom" 
+
+#As we would expect: + / += creates new objects
+#This is not the case when using any of the concat operators
+#i.e. .contact, <<
+1.9.3p125 :009 > full_name = nil 
+ => nil 
+1.9.3p125 :010 > full_name = first_name
+ => "Alex" 
+
+#Ruby internally makes full_name a *ptr to first_name
+1.9.3p125 :011 > full_name.object_id
+ => 70105840720680 
+1.9.3p125 :012 > first_name.object_id
+ => 70105840720680 
+
+#Concat will not break the *ptr to a new object like += does
+1.9.3p125 :013 > full_name.concat(last_name)
+ => "Alex Blom" 
+
+#Because the pointer was not broken, first_name has the expected value of full_name
+1.9.3p125 :014 > first_name
+ => "Alex Blom" 
+
+#Confirm it is still the same object
+1.9.3p125 :015 >   full_name.object_id
+ => 70105840720680 
+1.9.3p125 :016 > first_name.object_id
+ => 70105840720680 
+
+#The same will apply with other contact operators (i.e. <<)
+1.9.3p125 :017 > full_name = nil
+ => nil 
+1.9.3p125 :018 > first_name = "Alex" #full name is Alex Blom due to above
+ => "Alex" 
+1.9.3p125 :019 > first_name.object_id
+ => 70105706563920 
+1.9.3p125 :020 > full_name = first_name 
+ => "Alex" 
+1.9.3p125 :021 > full_name << last_name
+ => "Alex Blom" 
+1.9.3p125 :022 > first_name
+ => "Alex Blom" 
+
+#Full name will still be a *ptr to first_name
+1.9.3p125 :023 > full_name.object_id
+ => 70105706563920
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