"if"语句可处理多少"&&"？

Question

我有以下代码:

if @if_tannin_true && @if_acid_true && @if_alcohol_true && @if_body_true #I would like to add this: && @if_fruit_true #&& @if_fruit_character_true && @if_non_fruit_true && @if_organic_earth_true && @if_inorganic_earth_true && @if_wood_true

  y = 0
  while y < @grapes[i].testables.count
    @result << @grapes[i].testables[y].name
    y+=1
  end
end

我意识到使用四个"&&"的if语句可以正常工作,但是五分之一的语句不会.我该怎么处理？

---

编辑:它现在有效.我刚刚重启了服务器.很高兴知道我们可以根据需要使用尽可能多的"&&".

Answer 1

有趣的问题!

简短的回答

5000到10000之间,具体取决于您的系统.

理论

您可以创建一个包含许多字符串的字符串true && true && true && ...并对其进

• 如果它返回true,你可以添加更多的&&s.
• 如果它因故障SystemStackError或甚至是分段故障而失败,您将需要删除一些&&s.

由于它可能崩溃,您需要编写2个不同的脚本,以防止主循环崩溃.

bsearch 尽可能快地找到限制,而不必迭代每一个可能性.

码

many_ands.rb

# many_ands.rb
many_ands = (['true'] * (ARGV[0].to_i + 1)).join(' && ')
eval(many_ands)

max_ands.rb

big_number = 100_000

max_ands = (0..big_number).bsearch do |i|
  print "Testing #{i} : "
  result = system("ruby many_ands.rb #{i}")
  puts result ? 'Fine' : "Too many &&'s"
  puts
  !result
end

puts "Max number of &&'s without exception : #{max_ands - 1}"

它输出:

Testing 50000 : many_ands.rb:2:in `eval': stack level too deep (SystemStackError)
    from many_ands.rb:2:in `<main>'
Too many &&'s

Testing 25000 : many_ands.rb:2:in `eval': stack level too deep (SystemStackError)
    from many_ands.rb:2:in `<main>'
Too many &&'s

Testing 12500 : many_ands.rb:2:in `eval': stack level too deep (SystemStackError)
    from many_ands.rb:2:in `<main>'
Too many &&'s

Testing 6250 : many_ands.rb:2:in `eval': stack level too deep (SystemStackError)
    from many_ands.rb:2:in `<main>'
Too many &&'s

Testing 3125 : Fine

Testing 4688 : Fine

Testing 5469 : many_ands.rb:2:in `eval': stack level too deep (SystemStackError)
    from many_ands.rb:2:in `<main>'
Too many &&'s

Testing 5079 : Fine

Testing 5274 : many_ands.rb:2:in `eval': stack level too deep (SystemStackError)
    from many_ands.rb:2:in `<main>'
Too many &&'s

Testing 5177 : many_ands.rb:2:in `eval': stack level too deep (SystemStackError)
    from many_ands.rb:2:in `<main>'
Too many &&'s

Testing 5128 : many_ands.rb:2:in `eval': stack level too deep (SystemStackError)
    from many_ands.rb:2:in `<main>'
Too many &&'s

Testing 5104 : Fine

Testing 5116 : Fine

Testing 5122 : Fine

Testing 5125 : Fine

Testing 5127 : many_ands.rb:2:in `eval': stack level too deep (SystemStackError)
    from many_ands.rb:2:in `<main>'
Too many &&'s

Testing 5126 : many_ands.rb:2:in `eval': stack level too deep (SystemStackError)
    from many_ands.rb:2:in `<main>'
Too many &&'s

Max number of &&'s without exception : 5125

这取决于系统:在我的Linux VM上,它返回5125.在服务器上,它返回7930.

即使在同一系统上,结果也会因一次运行而异.

eval还是&&？

限制来自哪里？是从传递给它的字符串长度eval还是来自&&s 的数量？

通过修改many_ands.rb,我们现在将一个大字符串传递给eval,其中包含许多小表达式而不是一个巨大的&&表达式:

many_ands = (['true'] * (ARGV[0].to_i + 1)).join(';')
eval(many_ands)

主循环输出:

Testing 5000000 : Fine

Testing 7500000 : Fine

Testing 8750000 : Fine

Testing 9375000 : Fine

Testing 9687500 : Fine

Testing 9843750 : Fine

Testing 9921875 : Fine

Testing 9960938 : Fine

Testing 9980469 : Fine

Testing 9990235 : Fine

Testing 9995118 : Fine

Testing 9997559 : Fine

Testing 9998780 : Fine

Testing 9999390 : Fine

Testing 9999695 : Fine

Testing 9999848 : Fine

Testing 9999924 : Fine

Testing 9999962 : Fine

Testing 9999981 : Fine

Testing 9999991 : Fine

Testing 9999996 : Fine

Testing 9999998 : Fine

Testing 9999999 : Fine

Testing 10000000 : Fine

max_and.rb:11:in `<main>': undefined method `-' for nil:NilClass (NoMethodError)

似乎限制确实来自&&表达式中的s 数.有1000万true;...,传入的字符串eval是50MB大.