Using Ruby BinData gem to read choices

Question

I am implementing a data structure using Ruby and the BinData gem. I need to implement a Choice value. According to the BinData documentation, a choice can be implemented as:

class MyData < BinData::Record
  uint8  :type
  choice :data, :selection => :type do
    type key #option 1
    type key #option 2
  end
end

I need to have a default option in the choice:

class MyRecord < BinData::Record
    uint8 :type
    choice :mydata, :selection => :type do
            uint32 0
            uint16 1
    end
end

How can that be handled if type is not 0 or 1 in the above code?

I'm not sure this question makes any sense. What exactly do you need a "default" option for? — Mark Thomas, Jun 11 '11 at 11:48
I am sorry about the question been ambiguous. Edited and added some more code sample to clarify it further. — Indika K, Jun 12 '11 at 07:12
OK, I see what you're trying to do. Your own answer below looks like a good solution. Go ahead and accept it. — Mark Thomas, Jun 12 '11 at 12:23

score 5 · Answer 1 · answered Jun 20 '11 at 03:46

5

BinData 1.4.1 handles this natively with :default

class MyRecord < BinData::Record
  uint8 :data_type
  choice :mydata, :selection => :data_type do
    uint32 1
    uint16 2
    string :default, :read_length => 4
  end
end

answered Jun 20 '11 at 03:46

Dion Mendel

51
1

score 2 · Accepted Answer · edited Jun 14 '11 at 14:30

Well I found a work around. Anyway any other option is also most welcome.

class MyRecord < BinData::Record
    uint8 :data_type
    choice :mydata, :selection => :get_choice do
            uint32 1
            uint16 2
            string 255, :read_length => 4
    end

    def get_choice
            choices = [1, 2]
            if choices.include? data_type
                    return data_type
            else
                    return 255
            end
    end
end

score -1 · Answer 3 · answered Jun 14 '11 at 16:37

-1

you could set a default in a constructor perhaps...

answered Jun 14 '11 at 16:37

rogerdpack

62,887
36
269
388

Using Ruby BinData gem to read choices

3 Answers3