[rust] --gen-mutable support in rust timeline ?

[sundeepks]

Do we have API to in place mutation in rust ? currently using flatc (/snap/flatbuffers/191/bin/flatc) when I am generating code with --gen-mutable flag I do'n't see any generated code difference.

Wanted to perform in place mutation (Scalar values incremental updates) of bytes (stored in disk) & again persisting to disk

Any pointers on how to achieve the same using rust ?

[github-actions]

This issue is stale because it has been open 6 months with no activity. Please comment or this will be closed in 14 days.

[mleonhard]

I just discovered flatbuffers. Does this mean that flatc produces Rust code that cannot mutate flatbuffers?

[mleonhard]

Answering my own question:
"FlatBuffers supports both reading and writing FlatBuffers in Rust."
https://google.github.io/flatbuffers/flatbuffers_guide_use_rust.html

[kalyanmysore]

@mleonhard gen-mutable refers to a different concept.
Rust does allow you to create a flat buffer (i.e, serialize items to a block of bytes) and also allows you to read items out of such a serialized block of bytes.
However, the c++ implementation allows an ability to change (mutate) a scalar value in such a serialized block of bytes very efficiently. This feature allows very efficient programs that dont have to have (or have less of) other data structures (and memory access) to store dynamic state.
The issue is that rust does not yet support this (atleast, as far as I know). c++ supports it via the --gen-mutable compiler option.

[CasperN]

Rust support for in-place mutation is somewhat far away.

Current priorities are:

1. Better representation of enums
2. Verifier
3. Better story around untrusted data in general
4. object API
5. Mutation API

[ec1oud]

Why do you close it if it's "somewhat far away" but not impossible? I was also hoping to use that feature. Is C++ really the only language that has it?

[Buggaboo]

Do we have API to in place mutation in rust ? currently using flatc (/snap/flatbuffers/191/bin/flatc) when I am generating code with --gen-mutable flag I do'n't see any generated code difference.

Wanted to perform in place mutation (Scalar values incremental updates) of bytes (stored in disk) & again persisting to disk

Any pointers on how to achieve the same using rust ?

If you want memory stored on disk that reflects some kind of thread-safe memory pool (bar unbounded Vectors), you could look into mmap. In case of any mutations, e.g. a mutating worker thread, could use channels to pass on messages to any async receiver, to start reading the mutated data. Afaik, Builder and Table etc. don't care where they get their slice from.

[github-actions]

This issue is stale because it has been open 6 months with no activity. Please comment or label not-stale, or this will be closed in 14 days.

[github-actions]

This issue was automatically closed due to no activity for 6 months plus the 14 day notice period.