Fix inconsistent behavior from String#first/#last

While calling String#first or String#last with zero or a Fixnum < the
string's length returns a new string, a Fixnum >= the string's length
returns the string itself. This inconsistency can lead to inadvertent
mutation of a string.

1 files changed, 4 insertions, 4 deletions

diff --git a/activesupport/lib/active_support/core_ext/string/access.rb b/activesupport/lib/active_support/core_ext/string/access.rb
index 6018fd9641..ebd0dd3fc7 100644
--- a/activesupport/lib/active_support/core_ext/string/access.rb
+++ b/activesupport/lib/active_support/core_ext/string/access.rb
@@ -64,7 +64,7 @@ class String
 
   # Returns the first character. If a limit is supplied, returns a substring
   # from the beginning of the string until it reaches the limit value. If the
-  # given limit is greater than or equal to the string length, returns self.
+  # given limit is greater than or equal to the string length, returns a copy of self.
   #
   #   str = "hello"
   #   str.first    # => "h"
@@ -76,7 +76,7 @@ class String
     if limit == 0
       ''
     elsif limit >= size
-      self
+      self.dup
     else
       to(limit - 1)
     end
@@ -84,7 +84,7 @@ class String
 
   # Returns the last character of the string. If a limit is supplied, returns a substring
   # from the end of the string until it reaches the limit value (counting backwards). If
-  # the given limit is greater than or equal to the string length, returns self.
+  # the given limit is greater than or equal to the string length, returns a copy of self.
   #
   #   str = "hello"
   #   str.last    # => "o"
@@ -96,7 +96,7 @@ class String
     if limit == 0
       ''
     elsif limit >= size
-      self
+      self.dup
     else
       from(-limit)
     end