FLUID-6365: Create new construct, codenamed "gyres", to unify and replace the use of invokers and events

Description

These old-fashioned constructs suffer from very poor method combination capabilities as well as making unnecessary complexities for those who need to traffic in asynchronous values. We need a new, unifying construct, which arguably takes the form of a "very lightweight component" since it forms a scoping unit in which names can be resolved.

The old definitions would be "compiled" into the new form, much in the way that C's "structs" were grandfathered into C++ syntax as resugared kinds of "classes".

We codename this facility as "gyres" since the construct forms a small "swirl" in which names and values may locally follow each other about, until it is destroyed. We face the usual odd issue about when indeed we deallocate this thing - in the case it "compiles" to the effect of an old-fashioned method or invoker, we would obviously not allocate anything at all. In the case of a longer-lived gyre, it would be deallocated at the point that the lightweight IoC-like environment had made its last reference into it as a result of its final sequence step.

This development has been discussed and motivated at https://wiki.fluidproject.org/display/fluid/Plan+to+Abolish+Invokers+and+Events

Comments

• Antranig Basman commented 2020-12-15T11:47:31.724-0500

  Note: A further thing we have to achieve when we abolish listeners is to fully potentialise their registration - look at the following messy locution in the IoC testing framework to deal with the cases whether the listener target exists yet or not:

  bind = function (wrapped) {
                  // Push the distribution whether the component exists or not - since a further one may be created at this
                  // path via a createOnEvent annotation
                  var options = {};
                  fluid.event.identifyListener(wrapped);
                  fluid.set(options, ["listeners"].concat(analysed.path), {
                      listener: wrapped,
                      // Don't supply "args" here because we decode them ourselves in decodeListener
                      namespace: fixture.namespace,
                      priority: fixture.priority
                  });
                  id = fluid.pushDistributions(analysed.head, analysed.selector, fixture.event,
                      [{options: options, recordType: "distribution", priority: fluid.mergeRecordTypes.distribution}]
                  );
                  var existent = analysed.query();
                  if (existent.length === 1) {
                      // In addition, directly register the listener on any currently existing component
                      var event = fluid.getForComponent(existent[0], ["events"].concat(analysed.path));
                      event.addListener(wrapped, fixture.namespace, priority);
                  } else if (existent.length > 1) {
                      reject(" matched more than one component during bind: ", existent);
                  } // Note we do not reject on 0 matches since it may match via the distribution after construction
              };