如何在Ruby 2.7中的哈希数组上进行模式匹配？

问题描述

我正在通过针对new pattern matching feature in Ruby 2.7的模式匹配来试验JSON document。我想用它只匹配具有某些特征的数组元素。就我而言，有一系列区域数据存储为散列，每个散列都有一个ID。我只需要将id的{​​{1}}与哈希匹配，如下所示：

10

我希望它可以打印“我们发现了10区！”但事实并非如此。

是否可以使用Ruby模式匹配来做到这一点？

解决方法

u/zvero_kha有一个答案here。基本上，我正在寻找的被称为“查找模式”，并且只是最近才被合并到Ruby中。预计它将在Ruby 3.0版本中。在我的情况下，您将如何使用它：

case region_values
  # Note the "splat-like" asterisks. These are the "find patterns."
  in [*,{id: 10} => r10,{id: 11} => r11,*]
    puts "Region 10: #{r10}"
    puts "Region 11: #{r11}"
    # Note that both r10 and r11 are available in this block of code here
else
  puts 'aw shucks'
end

Matz's explanation对于使用这些“查找模式”非常有用。

,

我们发现给定的代码为region_values检索了以下值：

region_values
  #=> [
    {:region=>"Region01",:id=>1,:region_description=>"1 - Rockford Region Hospitals",:ICUAvail=>126,:ICUCapacity=>234,:VentsAvailable=>296,:VentsCapacity=>359},{:region=>"Region02",:id=>2,:region_description=>"2 - Peoria Region Hospitals",:ICUAvail=>140,:ICUCapacity=>304,:VentsAvailable=>398,:VentsCapacity=>496},{:region=>"Region03",:id=>3,:region_description=>"3 - Springfield Region Hospitals",:ICUAvail=>77,:ICUCapacity=>150,:VentsAvailable=>350,:VentsCapacity=>410},{:region=>"Region04",:id=>4,:region_description=>"4 - Edwardsville Region Hospitals",:ICUAvail=>61,:ICUCapacity=>113,:VentsAvailable=>134,:VentsCapacity=>158},{:region=>"Region05",:id=>5,:region_description=>"5 - Marion Region Hospitals",:ICUAvail=>64,:ICUCapacity=>107,:VentsAvailable=>294,:VentsCapacity=>309},{:region=>"Region06",:id=>6,:region_description=>"6 - Champaign Region Hospitals",:ICUAvail=>70,:ICUCapacity=>162,:VentsAvailable=>260,:VentsCapacity=>287},{:region=>"Region07",:id=>7,:region_description=>"7 - Southwest Suburbs Region Hospitals",:ICUAvail=>175,:ICUCapacity=>484,:VentsAvailable=>444,:VentsCapacity=>589},{:region=>"Region08",:id=>8,:region_description=>"8 - West Suburbs Region Hospitals",:ICUAvail=>176,:ICUCapacity=>480,:VentsAvailable=>319,:VentsCapacity=>550},{:region=>"Region09",:id=>9,:region_description=>"9 - Northwest Suburbs Region Hospitals",:ICUAvail=>238,:ICUCapacity=>452,:VentsAvailable=>438,:VentsCapacity=>533},{:region=>"Region10",:id=>10,:region_description=>"10 - Northeast Suburbs Region Hospitals",:ICUAvail=>112,:ICUCapacity=>206,:VentsAvailable=>190,:VentsCapacity=>234},{:region=>"Region11",:id=>11,:region_description=>"11 - City of Chicago Region Hospitals",:ICUAvail=>395,:ICUCapacity=>1064,:VentsAvailable=>1392,:VentsCapacity=>1803}
]

在发布此内容之前，我没有意识到Ruby v2.7中的新模式匹配功能。在阅读this article之后，我并没有真正看到这如何解决您的问题（尽管该功能本身很有趣并且似乎很有用）。您可以这样写：

region_values.each do |h|
  puts case h
  in {id: 10}
    'We found region 10!'
  else
    'aw shucks'
  end
end
aw shucks
aw shucks
aw shucks
aw shucks
aw shucks
aw shucks
aw shucks
aw shucks
aw shucks
We found region 10!
aw shucks

或

found = region_values.find do |h|
  case h
  in {id: 10}
    true
  end
end

puts found ? 'We found region 10!' : 'aw shucks'
We found region 10!

但新功能都不是非常有趣的应用。