A function decorator for telemetry.

Usage

defmodule MyApp.MyModule do
  use TelemetryDecorator

  @decorate telemetry([:my_app, :succeed])
  def succeed(arg1, arg2) do
    :...
  end
end

Because we're using :telemetry.span/3 under the hood, you'll get these events:

• [:my_app, :succeed, :start]
• [:my_app, :succeed, :stop]
• [:my_app, :succeed, :exception]

Because we're wrapping it with Decorator, we can provide more metadata than :telemetry.span/3 usually does:

• Any variables matched by your arguments for :start, :stop, and :exception events

• Your function's result for :stop events (overriding any variable named result)

To include more internal variables in your :stop events, add the include option:

defmodule MyApp.MyModule do
  use TelemetryDecorator

  def succeed(why), do: succeed(why, [])

  @decorate telemetry([:my_app, :succeed], include: [:type])
  def succeed(why, opts) do
    type = Keyword.get(opts, :type, :ok)
    {type, why}
  end
end

To watch :telemetry.span/3 style events at the iex> prompt:

handler_id = TelemetryDecorator.watch([:my_app, :succeed])
MyApp.MyModule.succeed(42)
# hang up, or explicitly unwatch:
TelemetryDecorator.unwatch(handler_id)

TelemetryDecorator.watch/1 sends to remote consoles, too, and with syntax colours. See the documentation for Pretty to find out how.