在Ruby中字符串是可变的吗？

在Ruby中字符串是可变的吗？按照惯例

创建一个值为“hello world”的新字符串对象

str = "hello"
str << " world"

str=“你好”
str是的，
“你好”
irb（主）：012:0>str.object\u id
=> 22269036
irb（主要）：013:0>str“你好，世界”
irb（主）：014:0>str.object\u id
=> 22269036
irb（main）：015:0>str=str+“世界”
=>“你好，世界”
irb（主）：016:0>str.object\u id
=> 21462360
irb（主要）：017:0>
作为补充，这种可变性的一个含义如下：

ruby-1.9.2-p0 :001 > str = "foo"
 => "foo" 
ruby-1.9.2-p0 :002 > ref = str
 => "foo" 
ruby-1.9.2-p0 :003 > str = str + "bar"
 => "foobar" 
ruby-1.9.2-p0 :004 > str
 => "foobar" 
ruby-1.9.2-p0 :005 > ref
 => "foo" 

及

是的，它们是：

x = "hallo"
x[1] = "e"

p x # "hello"

+为了演示如何确定对象是否确实相同或不同，有人能向我解释一下为什么这个答案被否决了吗？
ruby-1.9.2-p0 :001 > str = "foo"
 => "foo" 
ruby-1.9.2-p0 :002 > ref = str
 => "foo" 
ruby-1.9.2-p0 :003 > str = str + "bar"
 => "foobar" 
ruby-1.9.2-p0 :004 > str
 => "foobar" 
ruby-1.9.2-p0 :005 > ref
 => "foo" 

ruby-1.9.2-p0 :001 > str = "foo"
 => "foo" 
ruby-1.9.2-p0 :002 > ref = str
 => "foo" 
ruby-1.9.2-p0 :003 > str << "bar"
 => "foobar" 
ruby-1.9.2-p0 :004 > str
 => "foobar" 
ruby-1.9.2-p0 :005 > ref
 => "foobar" 

ruby-1.9.2-p0 :001 > "foo" == "foo"
 => true 
ruby-1.9.2-p0 :002 > "foo".object_id == "foo".object_id
 => false 
ruby-1.9.2-p0 :003 > :foo == :foo
 => true 
ruby-1.9.2-p0 :004 > :foo.object_id == :foo.object_id
 => true 

x = "hallo"
x[1] = "e"

p x # "hello"