handler<S, T> static method

T? handler<S, T>(
  1. void callback(
    1. S
    )?
)

Gets an event handler at the given key.

The event handler can be of any Function type, as specified by the type argument T.

When this method is called, the second argument, generator, is invoked. The generator callback must return a function, which we will call entrypoint, that matches the signature of T. The generator callback receives an argument, which we will call trigger. The entrypoint function must call trigger, optionally passing it any extra arguments that should be merged into the arguments specified in each event handler.

This is admittedly a little confusing. At its core, the problem is that this method cannot itself automatically create a function (entrypoint) of the right type (T), and therefore a callback (generator) that knows how to wrap a function body (trigger) in the right signature (T) is needed to actually build that function (entrypoint).

Implementation

static T? handler<S, T>(void Function(S)? callback) {
  if (callback == null) {
    return null;
  }
  throw 'Not implemented';
}