CODEWITHSUNDEEP
rubyexception
Asarluhi
Asarluhi

Reputation: 1290

How to use custom error messages

When I test my code with a non-numeric input, Ruby raises a default message. Instead, whenever an exception is raised, I would like my custom message to be printed with a default backtrace.inspect. I expect:

"oops... That was not a number"

to be raised instead of:

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

I wrote the code below, inspired by the following documentation: 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

The following code instead does behave as I expect; I can't see why the code below prints my default message while the code above does not:

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

Upvotes: 0

Views: 992

Answers (2)

Bunti
Bunti

Reputation: 1760

Simply modify your script like this.

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

Upvotes: 1

J&#246;rg W Mittag
J&#246;rg W Mittag

Reputation: 369428

Your unless condition can never be false: Kernel#Float will either raise an exception (in which case your condition isn't even reached) or return a Float (which is a subclass of Numeric).

Upvotes: 1

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