Ruby - 访问多维哈希并避免访问零对象

本文介绍了Ruby - 访问多维哈希并避免访问零对象的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 假设我尝试访问这样的哈希： my_hash ['key1'] ['key2'] ['key3'] 如果key1，key2和key3存在于散列表中，那么这很好，但是如果key1不存在呢？ 然后我得到 NoMethodError：undefined method [] for nil：NilClass 。 到目前为止，我正在处理这样一个条件如： if my_hash ['key1']&& my_hash ['key1'] ['key2'] ... 这是否合适？是否还有其他Rubiest方法？ 解决方案如果您使用Ruby 2.3或更高版本，您可以使用挖掘 my_hash.dig（'key1'，'key2'，'key3'） 很多人坚持使用普通的ruby，并链接&&< / code> guard测试。 / p> 您可以使用stdlib $ rel =noreferrer> Hash＃fetch 也是： my_hash.fetch（'key1'，{} ）.fetch（'key2'，{}）。fetch（'key3'，nil） 如链接ActiveSupport的 #try 方法。 my_hash.try（：[]，'key1'）。try（：[]，'key2'）。try（：[]，'key3'） 其他人使用 andand myhash ['key1'] .and and ['key2'] .andand [' key3'] 有些人认为自我中心nils 是一个好主意（尽管有人会狩猎你，如果他们发现你这样做会折磨你）。 class NilClass def method_missing（* args）;零; end end my_hash ['key1'] ['key2'] ['key3'] 您可以使用可枚举＃reduce （或别名注入）。 ['key1'，'key2'，'key3' ] .reduce（my_hash）{| m，k | m&& amp;&或者可能扩展哈希或只是你的目标哈希对象与嵌套查找方法 / p> module NestedHashLookup def nest * keys keys.reduce（self）{| m，k | m&& amp;& m [k]} 结束结束 my_hash.extend（NestedHashLookup） my_hash.nest'key1'，'key2'，'key3' 哦，我们怎么能忘记 maybe monad？ Maybe.new（my_hash）['key1'] ['key2'] ['key3'] Let's say I try to access a hash like this:my_hash['key1']['key2']['key3']This is nice if key1, key2 and key3 exist in the hash(es), but what if, for example key1 doesn't exist?Then I would get NoMethodError: undefined method [] for nil:NilClass. And nobody likes that.So far I deal with this doing a conditional like:if my_hash['key1'] && my_hash['key1']['key2'] ...Is this appropriate, is there any other Rubiest way of doing so? 解决方案 There are many approaches to this.If you use Ruby 2.3 or above, you can use digmy_hash.dig('key1', 'key2', 'key3')Plenty of folks stick to plain ruby and chain the && guard tests.You could use stdlib Hash#fetch too:my_hash.fetch('key1', {}).fetch('key2', {}).fetch('key3', nil)Some like chaining ActiveSupport's #try method.my_hash.try(:[], 'key1').try(:[], 'key2').try(:[], 'key3')Others use andandmyhash['key1'].andand['key2'].andand['key3']Some people think egocentric nils are a good idea (though someone might hunt you down and torture you if they found you do this).class NilClass def method_missing(*args); nil; endendmy_hash['key1']['key2']['key3']You could use Enumerable#reduce (or alias inject).['key1','key2','key3'].reduce(my_hash) {|m,k| m && m[k] }Or perhaps extend Hash or just your target hash object with a nested lookup methodmodule NestedHashLookup def nest *keys keys.reduce(self) {|m,k| m && m[k] } endendmy_hash.extend(NestedHashLookup)my_hash.nest 'key1', 'key2', 'key3'Oh, and how could we forget the maybe monad?Maybe.new(my_hash)['key1']['key2']['key3'] 这篇关于Ruby - 访问多维哈希并避免访问零对象的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！