Add metadata to exported functions#3682
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Add an optional string-to-string `metadata` dictionary to `export_function`/`exporter`, serialized into the `.mlxfn` header, and a `return_metadata` flag on `import_function` to read it back. This mirrors the existing `save_safetensors`/`load` metadata convention. The metadata is also exposed in C++ via `ImportedFunction::metadata()`. Closes ml-explore#2410
zcbenz
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Jun 16, 2026
| auto function_count = deserialize<int>(is); | ||
| ftable->shapeless = deserialize<bool>(is); | ||
| auto metadata_pairs = | ||
| deserialize<std::vector<std::pair<std::string, std::string>>>(is); |
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What would happen when importing functions exported from previous versions without metadata support? (There is no need to be compatible but I'm curious about the behavior)
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Proposed changes
This adds support for saving metadata along with an exported function, as requested in #2410.
mx.export_function(..., metadata={...})andmx.exporter(..., metadata={...})store adict[str, str]in the.mlxfnheader.mx.import_function(file, return_metadata=True)returns the imported function together with its metadata.ImportedFunction::metadata().I kept the metadata as a string-to-string dictionary to match the existing
save_safetensors/loadmetadata API. The issue mentioned possibly allowingUnion[str, int, float]values — happy to widen it if you'd prefer, but I went with string keys/values for consistency. Passingmetadatatogether with a callback raises, since it is only written when exporting to a file.Closes #2410
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