Lengths and other relations in data

[KOLANICH]

Is it possible to define a structure where the first field is the count (let's call it n) followed by array of n items of some smaller structure followed by the rest of structure.
In pseudo-c++

struct a{
//.....
};
struct b{
size_t count;
a data[count];
//rest of structure
}

Also variants are needed, where the type of field depends on combinational function of bit flags. For example if we process network packets, their content depends on the header. This can be japped to the language using polymophism.

[GreyCat]

Yeah, it's possible right now using repeat. The rough translation of your example in .ksy would be:

types:
  a:
    # .....
  b:
    seq:
      - id: count
        type: u4 # or whatever size_t maps to
      - id: data
        type: a
        repeat: expr
        repeat-expr: count

Conditionals are also supported. if is available in v0.5 (stable release, as of now), newer versions would include switch to avoid writing lots of ifs.

[KOLANICH]

OK, thank you.