BitLogger/docs/api/record-patch.md

name, group, category, update-time, description, key-word

name	group	category	update-time	description	key-word
record-patch	api	helper	20260613	Public patch function type used for record transformation before sink write.	patch record transform public

Record-patch

RecordPatch is the public function type used for record transformation. It represents any function that receives a Record and returns a new Record, and it is the shared shape behind helpers such as set_target(...), prefix_message(...), and append_fields(...).

Interface

pub type RecordPatch = @utils.RecordPatch

output

• RecordPatch - A function type equivalent to (Record) -> Record.

Explanation

Detailed rules explaining key parameters and behaviors

• This is a type alias, not a new runtime wrapper.
• Any function matching (Record) -> Record can be used wherever a RecordPatch is expected.
• Patches are used by Logger::with_patch(...), patch_sink(...), and helper constructors in patchers.mbt.
• The alias exists to make record-rewrite APIs clearer and easier to read in public signatures.

How to Use

Here are some specific examples provided.

When Need A Custom Record Rewrite Step

When a logger should rewrite each record before sink write:

let patch : RecordPatch = fn(rec) { rec.with_message("[custom] " + rec.message) }
let logger = Logger::new(console_sink()).with_patch(patch)

In this example, the alias makes the custom transformation shape explicit.

When Compose Existing Patch Helpers

When several reusable transformations should be combined:

let patch : RecordPatch = compose_patches([
  set_target("service.worker"),
  prefix_message("[worker] "),
])

In this example, the alias describes the common type returned by the patch helper constructors.

Error Case

e.g.:

• A patch that drops important fields or overwrites the target can change downstream observability unexpectedly.

• A patch that allocates heavily or copies too much data can add cost to every write path.

Notes

1. Use the alias when function signatures should communicate transformation intent clearly.

2. Helper constructors in patchers.mbt are usually preferable to handwritten patches for common cases.