chaokunyang commented on PR #1413:
URL: https://github.com/apache/incubator-fury/pull/1413#issuecomment-2016342416
I updated the implementation guide, the implementation for static languages
can use `switch/jump` for type evolution deserialization:
- Assume current type has `n` fields, peer type has `n1` fields.
- Generate an auto growing `field id` from `0` for every sorted field in
current type at the compile time.
- Compare the received type meta with current type, generate same id if the
field name is same, otherwise generate an
auto growing id starting from `n`, cache this meta at runtime.
- Iterate the fields of received type meta, use a `switch` to compare the
`field id` to deserialize data
and `assign/skip` field value. **Continuous** field id will be optimized
into `jump` in `switch` block, so it will
very fast.
Here is an example, suppose process A has a class `Foo` with version 1
defined as `Foo1`, process B has a class `Foo`
with version 2 defined as `Foo2`:
```c++
// class Foo with version 1
class Foo1 {
int32_t v1; // id 0
std::string v2; // id 1
}
// class Foo with version 2
class Foo2 {
// id 0, but will have id 2 in process A
bool v0;
// id 1, but will have id 0 in process A
int32_t v1;
// id 2, but will have id 3 in process A
int64_t long_value;
// id 3, but will have id 1 in process A
std::string v2;
// id 4, but will have id 4 in process A
std::vector<std::string> list;
}
```
When process A received serialized `Foo2` from process B, here is how it
deserialize the data:
```c++
Foo1 &foo1 = xxx;
std::vector<fury::FieldInfo> &field_infos = type_meta.field_infos;
for (auto &field_info : field_infos) {
switch (field_info.field_id) {
case 0:
foo1.v1 = buffer.read_varint32();
break;
case 1:
foo1.v2 = fury.read_string();
break;
default:
fury.skip_data(field_info);
}
}
```
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