userzhy opened a new pull request, #3064:
URL: https://github.com/apache/fory/pull/3064
## Why?
Go Fory lacks support for Union types, which prevents cross-language
serialization compatibility with other languages like C++, Java, Python, and
Rust that already support union/variant types. This limitation was reported in
issue #3031.
Without Union type support, Go users cannot:
- Serialize union types to communicate with other languages
- Use tagged union patterns common in serialization scenarios
- Leverage the full xlang serialization capabilities
## What does this PR do?
This PR implements complete Union type support for Go Fory by:
1. **Added TypeId constants** to `go/fory/types.go`:
- `UNION = 38` - for tagged union types
- `NONE = 39` - for empty/unit values
2. **Implemented Union struct and unionSerializer** in `go/fory/union.go`:
- `Union` struct that holds an `interface{}` value
- Serializes Union types by writing variant index + value
- Supports both internal Go mode and xlang mode (with type info)
- Properly dispatches to alternative type serializers
3. **Added RegisterUnionType API** to Fory:
- Allows users to register alternative types for a union
- Example: `f.RegisterUnionType(reflect.TypeOf(int32(0)),
reflect.TypeOf(""))`
4. **Added comprehensive tests** in `go/fory/union_test.go`:
- Basic types (int32, string, float64)
- Multiple alternative types
- Null/nil values
- Pointer types
- Bytes type
- Reference tracking mode
- Error cases (invalid alternatives, empty registration)
The implementation follows the same binary protocol as C++/Python/Rust
variant serialization:
1. Write variant index (varuint32)
2. In xlang mode, write type info for the active alternative
3. Write the value using the alternative's serializer
## Related issues
Fixes #3031
Related to #3027 (tracking issue for xlang union type system)
## Does this PR introduce any user-facing change?
- [x] Does this PR introduce any public API change?
- **Yes**: Adds `Union` struct and `RegisterUnionType` method. Users can
now use Union types in their code and they will be automatically
serialized/deserialized.
- This is backward compatible - existing code continues to work.
- [x] Does this PR introduce any binary protocol compatibility change?
- **No**: The implementation uses the existing TypeId.UNION (38) and
TypeId.NONE (39) defined in the specification.
- The binary protocol follows the same format as C++/Python/Rust
implementations.
- Existing serialized data is not affected.
## Benchmark
This PR does not have a performance impact on existing functionality:
- Union type handling only activates when Union types are actually used
- The implementation uses efficient type matching via reflection
- Variant index is encoded using varuint32 (compact encoding)
- No changes to existing serializers or hot paths
For Union types specifically, the overhead is minimal:
- One varuint32 write/read for the variant index
- One type dispatch (same as normal polymorphic serialization)
- No additional allocations beyond the Union struct itself
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