Ruby的Hash和ActiveSupport的HashWithIndifferentAccess之间的区别

Question

Ruby Hash和ActiveSupport有什么区别HashWithIndifferentAccess？动态哈希哪个最好？

Answer 1

下面是一个简单的例子,它将向您展示简单的ruby哈希和"ActiveSupport :: HashWithIndifferentAccess"之间的区别

• HashWithIndifferentAccess允许我们将哈希键作为符号或字符串进行访问

简单的Ruby哈希

$ irb
  2.2.1 :001 > hash = {a: 1, b:2}
    => {:a=>1, :b=>2} 
  2.2.1 :002 > hash[:a]
    => 1 
  2.2.1 :003 > hash["a"]
    => nil 

::的ActiveSupport HashWithIndifferentAccess

2.2.1 :006 >   hash = ActiveSupport::HashWithIndifferentAccess.new(a: 1, b:2)
NameError: uninitialized constant ActiveSupport
    from (irb):6
    from /home/synerzip/.rvm/rubies/ruby-2.2.1/bin/irb:11:in `<main>'
2.2.1 :007 > require 'active_support/core_ext/hash/indifferent_access'
 => true 
2.2.1 :008 > hash = ActiveSupport::HashWithIndifferentAccess.new(a: 1, b:2)
 => {"a"=>1, "b"=>2} 
2.2.1 :009 > hash[:a]
 => 1 
2.2.1 :010 > hash["a"]
 => 1 

• class HashWithIndifferentAccess继承自ruby"Hash"及以上特殊行为.

Answer 2

在 Ruby 哈希中：

hash[:key]
hash["key"]

是不同的。在HashWithIndifferentAccess顾名思义，您可以访问key两种方式。

引用官方文档对此：

实现一个散列，其中键 :foo 和 "foo" 被认为是相同的。

和

在整个编写界面（调用 []=、merge 等）中用作键时，内部符号会映射到字符串。此映射属于公共接口。例如，给定：

hash = ActiveSupport::HashWithIndifferentAccess.new(a: 1)

您可以保证密钥作为字符串返回：

hash.keys # => ["a"]