如何在Ruby中编写switch语句?


当前回答

Ruby使用case编写switch语句。

根据案例文件:

Case语句包含一个可选条件,该条件位于一个参数到case的位置,以及零个或多个when子句。与条件匹配的第一个when子句(或计算为布尔真值(如果条件为空)“wins”及其代码节执行。case语句的值是成功的when子句,如果没有这样的子句,则为nil。case语句可以以else子句结尾。当语句可以有多个候选值,用逗号分隔。

例子:

case x
when 1,2,3
  puts "1, 2, or 3"
when 10
  puts "10"
else
  puts "Some other number"
end

较短版本:

case x
when 1,2,3 then puts "1, 2, or 3"
when 10 then puts "10"
else puts "Some other number"
end

正如“Ruby的case语句-高级技术”所描述的Ruby case;

可用于范围:

case 5
when (1..10)
  puts "case statements match inclusion in a range"
end

## => "case statements match inclusion in a range"

可与Regex一起使用:

case "FOOBAR"
when /BAR$/
  puts "they can match regular expressions!"
end

## => "they can match regular expressions!"

可与Procs和Lambdas一起使用:

case 40
when -> (n) { n.to_s == "40" }
  puts "lambdas!"
end

## => "lambdas"

此外,还可以与您自己的匹配类一起使用:

class Success
  def self.===(item)
    item.status >= 200 && item.status < 300
  end
end

class Empty
  def self.===(item)
    item.response_size == 0
  end
end

case http_response
when Empty
  puts "response was empty"
when Success
  puts "response was a success"
end

其他回答

多值时和无值情况:

print "Enter your grade: "
grade = gets.chomp
case grade
when "A", "B"
  puts 'You pretty smart!'
when "C", "D"
  puts 'You pretty dumb!!'
else
  puts "You can't even use a computer!"
end

这里有一个正则表达式解决方案:

print "Enter a string: "
some_string = gets.chomp
case
when some_string.match(/\d/)
  puts 'String has numbers'
when some_string.match(/[a-zA-Z]/)
  puts 'String has letters'
else
  puts 'String has no numbers or letters'
end

如果您需要“小于”或“大于”:

case x
when 1..5
  "It's between 1 and 5"
when 6
  "It's 6"
when 7..1.0/0
  "It's equal or greater than 7"
when -1.0/0..0
  "It's equal or less than 0"
end

1.0/0等于Float::INFINITY,因此您可以使用自己喜欢的。

在Ruby 2.6之后,您可以使用Endless Ranges,在Ruby 2.7之后,您还可以使用Beginless Ranges,例如:

case x
when 1..5
  "It's between 1 and 5"
when 6
  "It's 6"
when (7..)
  "It's equal or greater than 7"
when (..0)
  "It's equal or less than 0"
end

Ruby使用case编写switch语句。

根据案例文件:

Case语句包含一个可选条件,该条件位于一个参数到case的位置,以及零个或多个when子句。与条件匹配的第一个when子句(或计算为布尔真值(如果条件为空)“wins”及其代码节执行。case语句的值是成功的when子句,如果没有这样的子句,则为nil。case语句可以以else子句结尾。当语句可以有多个候选值,用逗号分隔。

例子:

case x
when 1,2,3
  puts "1, 2, or 3"
when 10
  puts "10"
else
  puts "Some other number"
end

较短版本:

case x
when 1,2,3 then puts "1, 2, or 3"
when 10 then puts "10"
else puts "Some other number"
end

正如“Ruby的case语句-高级技术”所描述的Ruby case;

可用于范围:

case 5
when (1..10)
  puts "case statements match inclusion in a range"
end

## => "case statements match inclusion in a range"

可与Regex一起使用:

case "FOOBAR"
when /BAR$/
  puts "they can match regular expressions!"
end

## => "they can match regular expressions!"

可与Procs和Lambdas一起使用:

case 40
when -> (n) { n.to_s == "40" }
  puts "lambdas!"
end

## => "lambdas"

此外,还可以与您自己的匹配类一起使用:

class Success
  def self.===(item)
    item.status >= 200 && item.status < 300
  end
end

class Empty
  def self.===(item)
    item.response_size == 0
  end
end

case http_response
when Empty
  puts "response was empty"
when Success
  puts "response was a success"
end

由于switch-case始终返回单个对象,因此我们可以直接打印其结果:

puts case a
     when 0
        "It's zero"
     when 1
        "It's one"
     end

在您的环境中不支持正则表达式?例如,Shopify脚本编辑器(2018年4月):

[错误]:未初始化常量RegExp

一种变通方法,结合了前面在这里和这里介绍过的方法:

code = '!ADD-SUPER-BONUS!'

class StrContains
  def self.===(item)
    item.include? 'SUPER' or item.include? 'MEGA' or\
    item.include? 'MINI' or item.include? 'UBER'
  end
end

case code.upcase
when '12345PROMO', 'CODE-007', StrContains
  puts "Code #{code} is a discount code!"
when '!ADD-BONUS!'
  puts 'This is a bonus code!'
else
  puts 'Sorry, we can\'t do anything with the code you added...'
end

我在类方法语句中使用了or,因为||的优先级高于包括

如果您仍然喜欢使用||,即使在这种情况下或更可取,也可以改为使用:(item.include?“A”)||。。。。您可以在这个repl.it中测试它。