Have a way to represent the size of two equal data fields

[hchataing]

Two options that we talked about are:

packet TwoEqualFields {
  size_of_fields : 8,
  field_one : 8[size_of_fields],
  field_two : 8[size_of_fields],
}

packet TwoEqualFields {
  _elementsize_(data) : 8,
  data: 8[2][],  // Two variable-size byte-arrays that have the same size.
}

The benefit of elementsize is that we will need something like that for GATT.
The downside is that data and mask are not the same, so it would be nicer to be able to have meaningful names.

Two other options are:

packet TwoEqualFields {
  _size_(field_one) : 8,
  field_one : 8[],
  field_two : 8[_size_(field_one)],
}

packet TwoEqualFields {
  _size_(field_one) {, && ==} _size_(field_two) : 8,
  field_one : 8[],
  field_two : 8[],
}

[DeltaEvo]

What about

packet TwoEqualFields {
  _size_(field_one, field_two) : 8,
  field_one : 8[],
  field_two : 8[],
}

?

[gbonnefille]

From a strict user perspective, for readability, I vote for:

packet TwoEqualFields {
  size_of_fields : 8,
  field_one : 8[size_of_fields],
  field_two : 8[size_of_fields],
}

Furthermore, as many language, PDL should add a way to declare constants, for exemple where a length is share between multiple fields. With such extension in mind, having a literal inside the brackets is the most readable form.

const size_of_fields 3
packet TwoEqualFields {
  field_one : 8[size_of_fields],
  field_two : 8[size_of_fields],
}