Question

I am a newbie to Ruby and am learning it using “Programming Ruby 1.9” (PickAxe). In the book, I see a program which I modified thus:

 1 #!/usr/bin/env ruby -w
 2 
 3 class BookInStock
 4         attr_reader :isbn
 5         attr_accessor :price
 6         def initialize(isbn, price)
 7                 @isbn = isbn
 8                 @price = Float(price)
 9         end
10 #       def price=(price)
11 #               @price = Float(price)
12 #       end
13 end
14 
15 b1 = BookInStock.new("isbn1", 3)
16 p b1
17 b2 = BookInStock.new("isbn2", 3.14)
18 p b2
19 b3 = BookInStock.new("isbn3", "5.67")
20 p b3
21 b3.price = "10.32"
22 p b3

Line number 8 ensures that the right value is assigned to b3.price.

But how do I handle cases like line number 21 without using a method like in line 10-12?

Is there some way in which I can modify the attr_accessor for this? Or am I asking for too much 😀

I could not find any such references online.

Answer 1

attr_accessor :sym is a method of a Class that defines simple getter and setter methods.

You can define your own casting_attr_accessor:

class Class

 def casting_attr_accessor(accessor, type)

     define_method(accessor) do  
       instance_variable_get("@#{accessor}")
     end        

     define_method("#{accessor}=") do |val| 
       instance_variable_set("@#{accessor}", Kernel.send(type.to_s, val))
     end
 end
end

And then in your class use it like

casting_attr_accessor :price, Float