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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.
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1 parent 9935208 commit 9e67954dcfdc92f1087a03c0b1c61251d993e270 @ernie ernie committed Apr 18, 2014
@@ -64,7 +64,7 @@ def to(position)
# 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"
@@ -76,15 +76,15 @@ def first(limit = 1)
if limit == 0
''
elsif limit >= size
- self
+ self.dup
else
to(limit - 1)
end
end
# 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 @@ def last(limit = 1)
if limit == 0
''
elsif limit >= size
- self
+ self.dup
else
from(-limit)
end
@@ -296,6 +296,12 @@ class StringAccessTest < ActiveSupport::TestCase
assert_equal 'x', 'x'.first(4)
end
+ test "#first with Fixnum >= string length still returns a new string" do
+ string = "hello"
+ different_string = string.first(5)
+ assert_not_same different_string, string
+ end
+
test "#last returns the last character" do
assert_equal "o", "hello".last
assert_equal 'x', 'x'.last
@@ -308,6 +314,12 @@ class StringAccessTest < ActiveSupport::TestCase
assert_equal 'x', 'x'.last(4)
end
+ test "#last with Fixnum >= string length still returns a new string" do
+ string = "hello"
+ different_string = string.last(5)
+ assert_not_same different_string, string
+ end
+
test "access returns a real string" do
hash = {}
hash["h"] = true

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