default values for pointer fields are unsupported about capnpc-rust HOT 5 CLOSED

Could you elaborate a little bit on a) why and b) what that means?
Specifically, I get these warnings

warning: [UNSUPPORTED] Ignoring default value "" for text field foo. 
warning: [UNSUPPORTED] Ignoring non-null default for list field bar. 

for these fields

  foo @1: Text = "";
  bar @2: List(UInt32) = [];

from capnpc-rust.

Ah, good point. We probably shouldn't be emitting a warning when an explicit default matches whatever the implicit default would be.

These field definitions, with explicit defaults:

  foo @1: Text = "";
  bar @2: List(UInt32) = [];

have the same meaning as these definitions with implicit defaults:

  foo @1: Text;
  bar @2: List(UInt32);

In general, every field always has a default. The implicit default for a primitive field is zero. The implicit default for a list field is the empty list, and the implicit default for a struct field has a zeroed data section and an all-null pointer section.

For pointer fields, you can distinguish between "default" and "null" by using a has_foo() accessor. If you call get_foo() and the foo field contains a null pointer, you'll get the default value.

from capnpc-rust.

I've somewhat improved the situation here: 4216741

Unfortunately, it's not trivial to detect when the warning should be suppressed in the List and Struct cases.

from capnpc-rust.

Could you elaborate a little bit on a) why

The warning is to make sure you're aware that pointer defaults are currently unimplemented in capnpc-rust.

Of course, the long-term solution here is to actually implement pointer defaults. I think doing so should be fairly straightforward, but I haven't done it yet because I haven't needed to.

from capnpc-rust.

Fixed in: capnproto/capnproto-rust@f9ae25c

from capnpc-rust.