Question

我有一个哈希数组，我想写一个通用检查器，所以我想传入要检查的键的名称。散列是使用带冒号前缀（符号）的键定义的。我无法弄清楚如何正确使用变量作为键。即使密钥存在于散列中，使用变量访问它也会导致nil。如何通过变量访问哈希键？也许另一种问题是，我如何将变量强制转换为符号？

在IRB中，我这样做：

>> family = { 'husband' => "Homer", 'wife' => "Marge" }
=> {"husband"=>"Homer", "wife"=>"Marge"}
>> somevar = "husband"
=> "husband"
>> family[somevar]
=> "Homer"
>> another_family  = { :husband => "Fred", :wife => "Wilma" }
=> {:husband=>"Fred", :wife=>"Wilma"}
>> another_family[somevar]
=> nil
>>

Answer 1

您希望首先将字符串转换为符号：

another_family[somevar.to_sym]

如果您不想担心散列是符号还是字符串，只需将其转换为符号键

请参阅：How do I convert a Ruby hash so that all of its keys are symbols?

Answer 2

由于您的键是符号，因此请使用符号作为键。

> hash = { :husband => 'Homer', :wife => 'Marge' }
 => {:husband=>"Homer", :wife=>"Marge"}
> key_variable = :husband
 => :husband
> hash[key_variable]
 => "Homer"

Answer 3

您可以使用Active Support gem访问with_indifferent_access方法：

require 'active_support/core_ext/hash/indifferent_access'
> hash = { somekey: 'somevalue' }.with_indifferent_access
 => {"somekey"=>"somevalue"}
> hash[:somekey]
 => "somevalue"
> hash['somekey']
=> "somevalue"

Answer 4

如果您将Rails与ActiveSupport一起使用，请确实使用 HashWithIndifferentAccess 来灵活地访问带有字符串或符号的哈希。

family = HashWithIndifferentAccess.new({
  'husband' => "Homer", 
  'wife' => "Marge"
})

somevar = "husband"
puts family[somevar]
#Homer

somevar = :husband
puts family[somevar]
#Homer

Answer 5

你在散列中看到变量键的东西叫做Symbol是Ruby中的一个结构。它们主要用作散列键或引用方法名称。它们是不可变的，并且在给定时间只存在任何符号的一个副本，因此它们可以节省内存。

您可以将带有.to_sym或符号的字符串或符号转换为带.to_s的字符串来说明这一点让我展示这个例子：

strings = ["HTML", "CSS", "JavaScript", "Python", "Ruby"]
symbolArray = [:HTML, :CSS, :JavaScript, :Python, :Ruby]
# Add your code below!

symbols = Array.new
strings.each {|x|
 symbols.push(x.to_sym)
}

string = Array.new
symbolArray .each {|x|
 string.push(x.to_s)
}
print symbols
print string

结果将是：

[:HTML, :CSS, :JavaScript, :Python, :Ruby]
["HTML", "CSS", "JavaScript", "Python", "Ruby"]

在ruby 9.1中，你会在右边看到带冒号（:)的符号：

movies = { peter_pan: "magic dust", need_4_speed: "hey bro", back_to_the_future: "hey Doc!" }

我只是想让这一点变得更有说服力，所以谁能读到这个就可以了。

最后一件事，这是解决问题的另一种方法：

movie_ratings = {
  :memento =>  3,
  :primer => 3.5,
  :the_matrix => 3,

}
# Add your code below!

movie_ratings.each_key {|k| 
puts k.to_s
}

结果：

memento
primer
the_matrix

如何通过ruby中的变量访问冒号哈希键

5 个答案: