红宝石单元测试问题

Question

Have been trying to get the following code to work, but can't; it says I'm calling a private method.

What am I doing wrong?

    def subtotal(price, qty = 1)
      return nil if price.to_f<= 0 || qty.to_f <= 0
      price.to_f * qty.to_f
    end

    puts subtotal(12.93)
    puts subtotal(12.93, 3)
    puts subtotal(456.82, 6)

     def subtotal(qty = 1)
       return nil if price.to_f<= 0 || qty.to_f <= 0
       self.to_f * qty.to_f
     end

     book = 39.99
     car = 16789

     puts book.subtotal(3)
     puts car.subtotal
     puts car.subtotal(7)

Answer 1

Though I'd like more information, like the full class definition and the error trace, since the public method to_f is the only other method call here, I'm guessing that subtotal is defined as a private method.

In a Ruby class definition, keywords like public , protected , and private apply to all methods that come after the keyword. Check that the subtotal definition is not below private or protected in the class definition.

If not, then the issue likely lies elsewhere. Check that error trace, and look at where the error actually comes from.

Answer 2

Your subtotal works in two different environments.

One time, its a 'stand alone method', the other time it's a Numeric-method. So, lets define them as Numeric-method:

def subtotal(price, qty = 1)
  return nil if price <= 0 || qty <= 0
  price * qty
end

class Numeric
   def subtotal(qty = 1) #only one paramter. The other is 'self'
     return nil if self <= 0 || qty <= 0
     self * qty
   end
 end

puts subtotal(12.93)
puts subtotal(12.93, 3)
puts subtotal(456.82, 6)


 book = 39.99
 car = 16789

 puts book.subtotal(3)
 puts car.subtotal
 puts car.subtotal(7)

Remark on my code: I don't see a real reason for converting to Floats. If you start with Fixnums (see your car-example), then my solution works also. Perhaps, you need the conversion for your specific case.

From your example code I would prefer to define a Articcle class:

def subtotal(price, qty = 1)
  return nil if price <= 0 || qty <= 0
  price * qty
end

class Article
    def initialize(price = 0)
        @price = price
      end
   def subtotal(qty = 1)
     return nil if @price <= 0 || qty <= 0
     @price * qty
   end
 end

puts subtotal(12.93)
puts subtotal(12.93, 3)
puts subtotal(456.82, 6)


 book = Article.new(39.99)
 car = Article.new(16789)

 puts book.subtotal(3)
 puts car.subtotal
 puts car.subtotal(7)