chaokunyang commented on issue #3003:
URL: https://github.com/apache/fory/issues/3003#issuecomment-3690300932
## Implementation Progress
The `fory::field<>` template has been implemented with a refined API design
based on discussions. Here's a summary:
### Implemented Features
#### 1. Core API (`cpp/fory/meta/field.h`)
```cpp
namespace fory {
// Tag types
struct nullable {}; // Mark shared_ptr/unique_ptr as nullable
struct not_null {}; // Explicit non-null (for future pointer types like
weak_ptr)
struct ref {}; // Enable reference tracking (shared_ptr only)
template <typename T, int16_t Id, typename... Options>
class field { /* ... */ };
}
```
#### 2. Design Decisions
| Type | Default Nullable | Default Ref | Allowed Options |
|------|-----------------|-------------|-----------------|
| Primitives, `std::string` | **false** | false | **None** |
| `std::optional<T>` | **true** (inherent) | false | **None** |
| `std::shared_ptr<T>` | **false** | false | `nullable`, `not_null`, `ref` |
| `std::unique_ptr<T>` | **false** | false | `nullable` only |
#### 3. Compile-Time Validation
```cpp
// ✅ Valid usage
fory::field<std::string, 0> name;
fory::field<std::optional<int32_t>, 1> optional_age;
fory::field<std::shared_ptr<Node>, 2, fory::ref> parent;
fory::field<std::shared_ptr<Node>, 3, fory::nullable, fory::ref> link;
fory::field<std::unique_ptr<Data>, 4, fory::nullable> data;
// ❌ Compile errors
fory::field<int32_t, 0, fory::nullable> age; // nullable on
primitive
fory::field<std::unique_ptr<T>, 1, fory::ref> ptr; // ref on unique_ptr
fory::field<std::optional<T>, 2, fory::nullable> opt; // nullable on
optional
```
#### 4. Usage Example
```cpp
struct Document {
fory::field<std::string, 0> title;
fory::field<int32_t, 1> version;
fory::field<std::optional<std::string>, 2> description;
fory::field<std::shared_ptr<User>, 3> author; //
non-nullable
fory::field<std::shared_ptr<User>, 4, fory::nullable> reviewer; //
nullable
fory::field<std::shared_ptr<Node>, 5, fory::ref> parent; //
ref tracking
fory::field<std::shared_ptr<Node>, 6, fory::nullable, fory::ref> p; //
both
};
FORY_STRUCT(Document, title, version, description, author, reviewer, parent,
p);
```
### Files Created/Modified
#### New Files
- `cpp/fory/meta/field.h` - Core field template and type traits
- `cpp/fory/meta/field_test.cc` - 22 unit tests for field metadata
- `cpp/fory/serialization/field_serializer_test.cc` - 20 serialization
round-trip tests
#### Modified Files
- `cpp/fory/meta/BUILD` - Added `field_test` target
- `cpp/fory/meta/CMakeLists.txt` - Added `field.h` and test
- `cpp/fory/serialization/BUILD` - Added `field_serializer_test` target
- `cpp/fory/serialization/CMakeLists.txt` - Added test
- `cpp/fory/serialization/struct_serializer.h` - Integration with field
metadata
- `cpp/fory/serialization/type_resolver.h` - Field type unwrapping for
registration
### Test Results
All tests pass:
- 22 meta/field tests (type traits, field options, struct usage)
- 20 serialization tests (primitives, optional, shared_ptr, unique_ptr, ref
tracking, vectors)
### Deferred to Follow-up PR
The `FORY_FIELD_TAGS` macro (non-invasive API for existing structs) was
deferred due to complexity. The current implementation focuses on the
`fory::field<>` wrapper approach.
### Branch
Implementation is on branch `add_cpp_field_support`.
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