FluxTraining.Callback

			abstract type Callback

Supertype of all callbacks. Callbacks add custom functionality to
the training loop by hooking into different Events.Event s

Any Callback can be used by passing it to Learner . See
subtypes(FluxTraining.Callback) for implementations.

Extending

See Custom callbacks for a less
succinct tutorial format.

1. Create a struct MyCallback that subtypes FluxTraining.Callback .

2. Add event handlers by implementing methods for
   on (event, phase, callback, learner) . Methods should always
   dispatch on your callback, and may dispatch on specific Phases.Phase s
   and Events.Event s.

   For example, to implement an event handler that runs at the end of every
   step during training: on(::StepEnd, ::AbstractTrainingPhase, ::MyCallback, learner) .

3. Define what state the callback accesses and/or modifies by implementing
   stateaccess (::MyCallback) . While learner is always passed as an
   argument to on event handlers, by default a callback can not read or write
   to its fields. See stateaccess for more detail.

   If a callback needs to write some state that other callbacks should be able
   to access, it can store it in learner.cbstate if you add a permission in
   stateaccess .

4. If the callback needs some one-time initialization, you can implement init!
   which will be run at least once before any step is run.