Macros and Structs - the same API?

[Robert Gomulka]

Hi all,
I'm just trying out very promising construct library, which I've just discovered.

I'm reading the docs, but can't find some pieces.

I'm going to define some "data types". Like (example):
STRING = Struct("STRING",
                          UBInt8("length"),
                          Bytes("data", lambda ctx: ctx.length),
)

I am going to receive list of formats and list of data - I will then build them together.
Like:
data = [1, "str", 2]
formats = [UBInt8, STRING, UBInt8]

I'm not interested in the name, so for 1st and 3rd element it would be:
formats[n]('foo').build(data[n])
But the Struct is already initialized (right?) and I can't "call" it.
What's the way to achieve that?

Additionally, when composing Struct of smaller Structs I don't know how to do that:
BIGGER = Struct("name",
  UBInt8("something"),
  STRING,
  STRING)

^^ that will fail
How can I put several structs in one struct?

Regards,
Robert

[ceri...@gmail.com]

I am going to receive list of formats and list of data - I will then build them together.
Like:
data = [1, "str", 2]
formats = [UBInt8, STRING, UBInt8]

I'm not interested in the name, so for 1st and 3rd element it would be:
formats[n]('foo').build(data[n])
But the Struct is already initialized (right?) and I can't "call" it.
What's the way to achieve that?

Just pre-initialize an unsigned integer construct.

ubint8 = UBInt8("foo")

formats[n].build(data[n])

 

Additionally, when composing Struct of smaller Structs I don't know how to do that:
BIGGER = Struct("name",
  UBInt8("something"),
  STRING,
  STRING)

This code works for me.  What error are you seeing? 

[Robert Gomulka]

Thank you for your input.
I've been able to restructure the code to fix the issue in my code.
I've tried to use two strings with the same name:

STRING = Struct("STRING",
                          UBInt8("length"),
                          Bytes("data", lambda ctx: ctx.length),
)

BIGGER = Struct("name",
  UBInt8("something"),
  STRING,
  STRING)

BIGGER.parse('\x01' * 1000)
exception:

OverwriteError: 'STRING' would be overwritten but allow_overwrite is False

As said above, I was able to fix that by providing unique names. Sometimes they just look artificial, when I'm using the same structs alone, but I can live with that.

Regards,
Robert

[ceri...@gmail.com]

In general if you have unstructured data, you may want to use Sequence rather than Struct.  Sequence creates a ListContainer and doesn't require unique names for its subconstructs.

[Arek Bulski]

Gosh, you are reinventing PascalString.