# `Outboxer.Relay.Function`
[🔗](https://github.com/epinault/outboxer/blob/v0.1.0/lib/outboxer/relay/function.ex#L1)

A relay that calls a function for every message.

Useful for custom sinks, for wiring Outboxer to something that has no
dedicated relay, and for trying the library out.

    {Outboxer,
     repo: MyApp.Repo,
     outboxes: [
       audit: [relay: {Outboxer.Relay.Function, fun: &MyApp.Audit.forward/1}]
     ]}

## Options

  * `:fun` (required) - a 1-arity function, or an `{module, function, extra_args}`
    tuple called as `apply(module, function, [envelope | extra_args])`. It
    receives an `Outboxer.Envelope` and returns `:ok`, `{:ok, term}` or
    `{:error, reason}`. Raising counts as an error.

Messages are delivered one at a time, in order, and a failure blocks the
rest of that message's group (see `Outboxer.Relay.sequential/2`).

Prefer an MFA or a named capture (`&Mod.fun/1`) over an anonymous function
when the supervisor options come from config files.

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*Consult [api-reference.md](api-reference.md) for complete listing*