带有 NoMethodError 的 ruby​​ 代码

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:in `sort': undefined method `' for false:FalseClass (NoMethodError)

该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

这个to_int 方法将返回真或假。所以当你运行这行代码时：ar.map(&:to_int).sort，map 方法会将整个数组映射为真或假。

你的数组看起来像[false,false,true,false]，当你运行sort 函数时它会失败。

我不确定to_int函数的用途是什么，你只需要用简单的to_i函数映射，然后排序。

ar.map!(&:to_i).sort

确保使用map!，以便修改原始数组。

如果您确实将数组映射为整数，则必须将打印行修改为

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

否则会报错：

字符串不能被强制转换为 Fixnum

Answer 3

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

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

#!/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 ""

您似乎正在尝试按数字顺序打印参数。 这可以通过

来完成

puts ARGV.sort_by(&:to_i).join(" ")