Question

运行以下Ruby代码时：

#!/usr/bin/env ruby
ar=[]

class String
   def to_int
     self == self.to_i
   end
end

ARGV.each do |a|
  ar.push("#{a}")
end

ar.map(&:to_int).sort

ar.each do |x|
  print x + " "
end

puts ""

我收到以下错误：

example.rb：14：在`sort＆＃39 ;: undefined method`＆lt; =＆gt;＆＃39; for false：FalseClass（NoMethodError）

此程序需要使用带有数字列表的命令行参数运行。任何帮助将不胜感激。

Answer 1

ARGV.sort.each { |x| print x + " " }
puts

Answer 2

class String
   def to_int
     self == self.to_i
   end
end

此to_int方法将返回true或false。因此，当您运行此行：ar.map(&:to_int).sort时，map方法会将整个数组映射为true或false。

您的数组看起来像[false,false,true,false]，当您运行sort函数时，它将失败。

我不确定to_int函数的用途是什么，您只需要使用简单的to_i函数进行映射，然后对其进行排序。

ar.map!(&:to_i).sort

确保使用map!，以便修改原始数组。

如果您将数组映射为整数，则必须将打印行修改为

ar.each do |x| 
  print x.to_s + " "
end

否则您将收到错误：

字符串无法强制进入Fixnum

Answer 3

当我使用Ruby 2.3.0运行时，我没有收到该错误。我尝试过Ruby 2.0.0p648（OS X附带），2.1.5和2.2.4，它们也没有引发错误。

我有点不清楚你要在这里完成什么。你做的事情没有任何意义，但我会假设你正在尝试学习Ruby而你只是尝试不同的事情。

if(line.toLowerCase().contains("skype")) {
    // do what you want if skype is running
} else {
    // do what you want if skype is not running
}

您似乎正在尝试按照数字顺序打印参数。这可以通过

完成

#!/usr/bin/env ruby
ar=[]

# This is "monkey patching" String, and is a bad practice.
class String
  # A method named "to_int" implies a conversion to integer. But the "to_i" method already does
  # that, and this method doesn't convert to an integer, it converts to a boolean.
   def to_int
     # Comparing the string to itself as an integer. Why would it ever be true?
     self == self.to_i
   end
end

# I'm assuming that this is intended to convert the argument list to a list of strings.
# But ARGV should already a list of strings.
# And this would be better done as `ar = ARGV.map(&:to_s)`
ARGV.each do |a|
  ar.push("#{a}");
end

# This creates an array of values returned by `to_int`, then sorts the array.
# Since `String#to_int` (defined above) returns booleans, it's an array of "false" values, so
# sorting does nothing. But then the value of the `sort` is ignored, since it's not assigned to
# a variable. If you want to modify the order of an existing array, use `sort!`.
# But if you're trying to sort the array `ar` by the numeric values, `ar.sort_by(&:to_i)` would
# do that.
ar.map(&:to_int).sort

ar.each do |x| print x + " "; end

puts ""

带有NoMethodError的ruby代码

3 个答案: