From: Markus Fischer <markus@...>
Date: 2009-06-13T20:54:19+09:00
Subject: bit-struct feedback (was: Re: binaryparse: length in bytes of block definition?)

Hello Joel,

I've now rewritten my code to take advantage of you latest 0.12 changes
and have to say that it was a very pleasing experience. Everything
worked out of the box and the addition of the IO object was a real time
safer in moving from binaryparser to be bit-struct-only.

During this rewrite-session I made some notes how my further bit-struct
experience went. If you're annoyed by them, simply ignore 'em ;-)

* Allow block also for "nest" ?

It may sound redundant in the first place, but when it's just for
providing more structure without requiring an extra class definition, it
could be useful:

  class Foo < BitStruct
    nest :coord do
      signed :x, 8
      signed :y, 8
    end
  end

  Foo.new.coord.x


* Is explicit :length for vector necessary?

  class Tag < BitStruct
    signed  :flags, 32
    vector  :axis, Vec, :length => 3
  end

compared to

  class Tag < BitStruct
    signed  :flags, 32
    vector  :axis, Vec, 3
  end

Or am I missing any ambiguities because of the simple cases?


* Allow length not only in bits, but also bytes?

In my cases I've never encountered a situation where I needed a member
of a structure to represent anything which is not on a byte boundary.

All my signed and unsigned int have to read "32" (32bit, 4bytes) all
over the place. For strings I'm writing "64*8" for string with 64
characters.

How about a new default_option :granularity which is "1" by default.
When set to "8", every specified length (except for vector ...) is
multiplied by that factor before used?


* Why "vector" and not just "array"?

I'm getting pretty confused all the time due the term vector :) I'm
always thinking about graphical vectors, etc. For, me arrays would also
better describe the environment how the data is used (array of ints ..
vector of ints ... ?).

Joel VanderWerf wrote:
> Markus Fischer wrote:
>> C-struct example:
>>
>> typedef struct {
>> 	float		normal[3];
>> 	float		dist;
>> } dplane_t;
>>
>> Ruby (?):
>>
>> class MyFloat < BitStruct
>>   float :value, 32
>> end
>>
>> class Plane < BitStruct
>>   vector :normal, MyFloat, :length => 3
>>   float :dist, 32
>> end
> 
> and then
> 
>    Plane.new.normal[2].value

As you said, looks like one layer to much. Thanks for your block-support
to vector, could this maybe be detected for simple cases?

  class Plane < BitStruct
    vector :normal, :length => 3 do
      signed 32
    end
  end

I.e., having only one element and deliberately skip the naming to be
prepared for

  Plane.new.normal[2]


> As you can see, the reader method is fine, but the writer has to be
> broken down into a sequence of writes to each nested chunk... yuck.
> 
> The reason it doesn't allow simply
> 
>    md.row[2].col[7].x = 1.23
[...]
> 
> Any other ideas...?

Unfortunately not at this time. I'm using bit-struct solely for reading
binary data ATM and not creating them.


thanks,
- Markus