如何使用自定义错误消息

Question

当我使用非数字输入测试我的代码时，Ruby 会引发一条默认消息。相反，每当引发异常时，我希望我的自定义消息使用默认的backtrace.inspect 打印。我期望：

"oops... That was not a number"

被提升而不是：

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

受以下文档的启发，我编写了以下代码： 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

以下代码的行为确实符合我的预期；我不明白为什么下面的代码会打印我的默认消息，而上面的代码却没有：

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

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

Answer 2

您的unless 条件永远不会为假：Kernel#Float 将引发异常（在这种情况下甚至未达到您的条件）或返回Float（它是Numeric 的子类）。