C#: build failure - unable to convert optional to instance int

[heinermann]

Version: 0.11

meta:
  id: csharp_optionalcast
  endian: le

seq:
  - id: version
    type: u1
  - id: cnt_old
    type: s1
    if: version <= 96
  - id: cnt_new
    type: b12
    if: version > 96

instances:
  count:
    value: |
      version <= 96 ? cnt_old : cnt_new

Generates

_count = (int) ((Version <= 96 ? CntOld : CntNew));

Where

        private sbyte? _cntOld;
        private ulong? _cntNew;

with errors:

error CS0029: Cannot implicitly convert type 'sbyte?' to 'int'
error CS0029: Cannot implicitly convert type 'ulong?' to 'int'

Similarly, same issue if a b1 is used as a secondary condition where the condition for the b1 existing is the same as the first condition, i.e.

meta:
  id: csharp_optionalcast
  endian: le

seq:
  - id: version
    type: u1
  - id: has_more
    type: b1
    if: version > 96
  - id: more
    type: b2
    if: version > 96
  - id: old_stuff
    type: u1
    if: version <= 96

instances:
  count:
    value: |
      version <= 96 ? old_stuff :
      has_more ? more + 99 : more

[generalmimon]

Now I realize that I have encountered this problem a bunch of times in https://github.com/kaitai-io/coreldraw_cdr.ksy/search?q=C%23&type=commits. For anyone blocked by this bug, the general workaround is to use the typecasting .as<> operator to cast the optional value to the exact type it should seemingly already have (which will effectively drop the nullability of the type):

seq:
  - id: version
    type: u1
  - id: cnt_old
    type: s1
    if: version <= 96
  - id: cnt_new
    type: b12
    if: version > 96

instances:
  count:
    value: |
      version <= 96 ? cnt_old.as<s1> : cnt_new.as<b12>

It seems that there hasn't been any issue specifically talking about this error until now, so thanks for reporting.

Nevertheless, there are several related issues:

• C# Nullable support #758
• Extended nullabillity support for Kotlin and other null-safe languages #1111
• Value instances depending on nullable elements don't generate proper code #942