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# Type Alias Nemo Relay Free Fn

> Optional destructor for user data passed to callbacks. Called when the runtime no longer needs the associated callback.

Generated from `cargo doc --no-deps -p nemo-relay -p nemo-relay-adaptive -p nemo-relay-pii-redaction -p nemo-relay-ffi -p nemo-relay-types -p nemo-relay-plugin -p nemo-relay-worker-proto -p nemo-relay-worker`.

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Optional destructor for user data passed to callbacks. Called when the runtime no longer needs the associated callback.

Middleware callbacks may run concurrently on Relay runtime or publication threads. Callers must keep `user_data` valid and thread-safe until this destructor runs.

## Aliased Type

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## Variants

### `None`

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No value.

### `Some(unsafe extern "C" fn(*mut c_void))`

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Some value of type `T`.