Question

这是什么缩短版本？：

from = hash.fetch(:from)
to = hash.fetch(:to)
name = hash.fetch(:name)
# etc

注意fetch，如果密钥不存在，我想引发错误。

必须有更短的版本，例如：

from, to, name = hash.fetch(:from, :to, :name) # <-- imaginary won't work

如果需要，可以使用ActiveSupport。

Answer 1

使用哈希的values_at方法：

from, to, name = hash.values_at(:from, :to, :name)

对于散列中不存在的任何键，这将返回nil。

Answer 2

Ruby 2.3最后为哈希引入了fetch_values方法，直接实现了这一点：

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            <link href="https://cdnjs.cloudflare.com/ajax/libs/nvd3/1.7.0/nv.d3.min.css" rel="stylesheet" />
            <script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.5/d3.min.js"></script>
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                .datum(datum)
                .transition().duration(500)
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                .call(chart);
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Answer 3

hash = {from: :foo, to: :bar, name: :buz}

[:from, :to, :name].map{|sym| hash.fetch(sym)}
# => [:foo, :bar, :buz]
[:frog, :to, :name].map{|sym| hash.fetch(sym)}
# => KeyError

Answer 4

my_array = {from: 'Jamaica', to: 'St. Martin'}.values_at(:from, :to, :name)
my_array.keys.any? {|key| element.nil?} && raise || my_array

这会引发您所要求的错误

 my_array = {from: 'Jamaica', to: 'St. Martin', name: 'George'}.values_at(:from, :to, :name)
 my_array.keys.any? {|key| element.nil?} && raise || my_array

这将返回数组。

但OP要求失败的钥匙失败......

class MissingKeyError < StandardError
end
my_hash = {from: 'Jamaica', to: 'St. Martin', name: 'George'}
my_array = my_hash.values_at(:from, :to, :name)
my_hash.keys.to_a == [:from, :to, :name] or raise MissingKeyError
my_hash = {from: 'Jamaica', to: 'St. Martin'}
my_array = my_hash.values_at(:from, :to, :name)
my_hash.keys.to_a == [:from, :to, :name] or raise MissingKeyError

Answer 5

我想要的最简单的事情就是

from, to, name = [:from, :to, :name].map {|key| hash.fetch(key)}

或者，如果您要使用values_at，则可以使用带有默认值块的Hash：

hash=Hash.new {|h, k| raise KeyError.new("key not found: #{k.inspect}") }
# ... populate hash
from, to, name = hash.values_at(:from, :to, :name) # raises KeyError on missing key

或者，如果你如此倾向，那么猴子补丁Hash

class ::Hash
  def fetch_all(*args)
    args.map {|key| fetch(key)}
  end
end
from, to, name = hash.fetch_all :from, :to, :name

Answer 6

您可以使用默认值KeyError对象初始化哈希值。如果您尝试获取的密钥不存在，这将返回KeyError的实例。您需要做的就是检查它的（值）类，如果它是一个KeyError，则引发它。

hash = Hash.new(KeyError.new("key not found"))

让我们为这个哈希添加一些数据

hash[:a], hash[:b], hash[:c] = "Foo", "Bar", nil

最后查看值并在未找到密钥时引发错误

hash.values_at(:a,:b,:c,:d).each {|v| raise v if v.class == KeyError}

当且仅当密钥不存在时，这将引发异常。如果您有一个nil值的密钥，它不会抱怨。

Answer 7

模式匹配是Ruby 2.7中的一项实验功能。

hash = { from: 'me', to: 'you', name: 'experimental ruby' }

hash in { from:, to:, name: }

请参见https://rubyreferences.github.io/rubyref/language/pattern-matching.html

如何一次获取多个哈希值？

7 个答案: