Accessing multiple fields

[KOLANICH]

Sometimes a one needs to test thet the record is a terminator. Sometimes terminator is the record containing only zeros. How can we implement this?
1 We can test all the fields that they are zeros. For these we need a syntax allowing this. The most flexible way to do this is to match their names against a regex:

- id: test
  type: a
  repeat: until
  repeat-until: _./.+/

2 another way is to have a syntax to match binary representation. For that we need to have an operator to convert a field into binary and some language to create a sequence of zero bytes.

repeat-until: _.to_binary() == [0x00]*sizeof(a)

IMHO it's nice to have both.

[GreyCat]

"Only zeroes" is, unfortunately, a pretty vague definition. I don't really see any major benefits in "matching their names against a regex":

• I have no idea what _./.+/ is supposed to mean, or why is that supposed to mean "record containing only zeros".
• We have seq attributes, parse instances, value instances, parameters — why would all of them must be zeroes?
• How do we match non-integer data types (i.e. booleans, strings, byte buffers) against "zeroes"?
• I sincerily doubt that any of real-life parsers ever do that. In reality, 100% of manually rolled parsers that I've seen usually only check 1 or 2 significant fields.

another way is to have a syntax to match binary representation

Probably possible in some cases. I suggest that we'd return to this after implementation of #44.

[KOLANICH]

I have no idea what _./.+/ is supposed to mean, or why is that supposed to mean "record containing only zeros".

_. is a regular access to subproperties of last parsed element
"/.+/" is the regex matching any string without /n. So
_./.+/ means every property with any name (just any property) from the element

And I'm mistaken. The right condition should be

repeat-until: _./.+/ == 0

We have seq attributes, parse instances, value instances, parameters — why would all of them must be zeroes?

It should be configurable. By default is should match only the properties in ``seq```.

How do we match non-integer data types (i.e. booleans, strings, byte buffers) against "zeroes"?

to_binary()

I sincerily doubt that any of real-life parsers ever do that. In reality, 100% of manually rolled parsers that I've seen usually only check 1 or 2 significant fields.

In some reverse-engineered (from source) specs it is written to do so. And the parser in that repo really does so (and in a bit inefficient way, not sure that compilers can optimize that away).