冻结Ruby中的变量不起作用 [英] Freezing variables in Ruby doesn't work

问题描述

我正在学习Ruby，当将Object#freeze方法与变量一起使用时，我刚刚发现了有趣的行为.

I am learning Ruby, and I just found interesting behaviour when using the Object#freeze method with variables.

冻结变量(Fixnum或Array)之后，我仍然可以对其进行修改！奇怪，因为就我而言，这不应该发生，并且应该提高TypeError.

After I freeze a variable (either Fixnum or Array), I am still able to modify it! It is strange, since as far as I am concerned this should not happen and TypeError should be raised.

这是我的代码:

test = 666
var = 90
#ok
var += 5

puts "var.frozen? #{var.frozen?}"    
var.freeze    
puts "var.frozen? #{var.frozen?}"

var = test
puts "var = #{var}"

对于数组也是如此:

test = [666]
var = [90]
#ok
var += [5]

puts "var.frozen? #{var.frozen?}"    
var.freeze    
puts "var.frozen? #{var.frozen?}"

var = test
puts "var = #{var}"

但是当我尝试在冻结后将某些内容推入数组时，它会产生一个错误，正如预期的那样:

But when I try to push something into the array after freezing, it raises an arror, as expected:

test = [666]
var = [90]
#ok
var += [5]

puts "var.frozen? #{var.frozen?}"    
var.freeze    
puts "var.frozen? #{var.frozen?}"

var << test
puts "var = #{var}"

有人可以向我解释这个问题吗?看起来很奇怪.

Can somebody explain to me this issue? It seems strange.

编辑我正在使用Windows XP + Ruby 1.9.3-p429

Edit I am using Windows XP + Ruby 1.9.3-p429

推荐答案

您冻结对象，而不是变量，即，您无法更新冻结的对象，但可以将新对象分配给相同的变量.考虑一下:

You freeze objects, not variables, i.e. you can't update a frozen object but you can assign a new object to the same variable. Consider this:

a = [1,2,3]
a.freeze
a << 4
# RuntimeError: can't modify frozen Array

# `b` and `a` references the same frozen object
b = a
b << 4    
# RuntimeError: can't modify frozen Array

# You can replace the object referenced by `a` with an unfrozen one
a = [4, 5, 6]
a << 7
# => [4, 5, 6, 7]

顺便说一句:冻结Fixnum完全是没有用的，因为它们是不可变的对象.

As an aside: it is quite useless to freeze Fixnums, since they are immutable objects.

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