Question

当我使用非数字输入测试代码时，Ruby会引发默认消息。相反，每当引发异常时，我都希望使用默认的backtrace.inspect打印我的自定义消息。我期待：

"oops... That was not a number"

而不是：

invalid value for Float(): "h\n" (ArgumentError)

我编写了以下代码，受以下文档的启发： stackoverflow， rubylearning， github

class MyCustomError < StandardError
  def message
    "oops... That was not a number"
  end
end

def print_a_number
  begin
    puts "chose a number"
    number = Float(gets)
    raise MyCustomError unless number.is_a? Numeric
    puts "The number you chose is #{number}"
  rescue MyCustomError => err
    puts err.message  
    puts err.backtrace.inspect  
  end  
end

以下代码确实表现得像我期望的那样;我无法理解为什么下面的代码打印我的默认消息，而上面的代码没有：

class MyCustomError < StandardError
  def message
    "The file you want to open does not exist"
  end
end

def open_a_file

  begin
    puts "What file do you want to open?"
    file2open = gets.chomp

    raise MyCustomError unless File.file?(file2open)

    File.open(file2open, 'r') { |x|  
            while line = x.gets 
                puts line
            end
        }

  rescue MyCustomError => err
    puts err.message
    puts err.backtrace.inspect

  end
end

Answer 1

您的unless条件永远不会为假：Kernel#Float会引发异常（在这种情况下甚至无法达到您的条件）或返回Float（这是一个子类） Numeric）。

Answer 2

只需像这样修改你的脚本。

class MyCustomError < StandardError
  def message
    "oops... That was not a number"
  end
end

def print_a_number
  begin
    puts "chose a number"
    number = Float(gets) rescue false
    raise MyCustomError unless number.is_a? Numeric
    puts "The number you chose is #{number}"
  rescue MyCustomError => err
    puts err.message
    puts err.backtrace.inspect
  end
end

如何使用自定义错误消息

2 个答案: