[Rust] Struct Performance Optimization

[chaokunyang]

Feature Request

No response

Is your feature request related to a problem? Please describe

Currently fory rust have a buffer bound check for each struct field, but for numeric fields, the max possible binary length can be computed in advance at macro processing time. So we can compute max possible length in advance and grow buffer once, then write to buffer directly, and commit writer index after all numeric/bool fields has been written

Describe the solution you'd like

Take java/c++ struct fields serialization as reference:

• java: BaseObjectCodecBuilder.java
• C++: struct_serializer.h

Describe alternatives you've considered

No response

Additional context

No response

[Geethapranay1]

hi @chaokunyang

I tried optimizing struct field serialization by reserving buffer space upfront.

At proc macro expansion time, I compute a rough max size for primitive fields. For example, varint32 as 5 bytes, f64 as 8, bool as 1, etc.

Then before writing anything, I call context.writer.reserve(total) once.

For fixed size types like bool, i16, f32, f64, I switched to write_*_unchecked() to avoid repeated capacity checks.

For variable length ones like varint32, varint64, tagged_u64, I kept the checked writes since their size depends on values.

This is similar to how struct_serializer.h does it in C++. Precompute size, grow buffer, then write.

Wire fmt stays unchanged and tests are passing.

is this makes sense? can i do pr?

[chaokunyang]

For variable length ones like varint32, varint64, tagged_u64: you should write to buffer directly and accumlate writer index locally ,then commit writer index only once

[Geethapranay1]

got it. I'll add unchecked varint writes that track offset locally and commit the writer index once at the end.