Wildcard Handlers

One of the principle Motivations behind the TAO is to build Systems and Applications that are fundamentally designed to Evolve by using the concepts behind Aspect-Oriented Programming (AOP).

Most implementations of AOP use something to inject code

Wildcard Handlers allow us to add handlers to the TAO that are called when any of the Concrete trigram aspects match the Application Context set on the TAO.

This is one feature that sets tao.js apart from any other Event-driven mechanisms by allowing a Subscriber (handler) to subscribe to Events (AppCons) of any kind along a specific axis or axes (or none) in order to react over a broad spectrum of similar Events.

Wildcard Handlers can choose to focus on a specific Term, Action, or Orientation or some subset of those 3 or none at all.

Wildcard vs Concrete

Concrete trigram aspects are specifically named Terms, Actions or Orientations. They are called "Concrete" in that they are set and do not change to be something else.

For example: in {App,Enter,Portal}, the entire trigram is considered a Concrete Application Context because it specifically defines each aspect of the trigram for the Application Context. Each specifically defined aspect of the trigram is itself a Concrete Aspect, in this case a Concrete Term, Concrete Action and Concrete Orient(ation).

Wildcard trigrams are those that leave one or more of the trigram aspects undefined or "not Concrete."

What Wildcard trigrams look like

Wildcard trigrams can be defined in various different ways, the majority of which is to simply leave the trigram property out.

Example basic Wildcard trigrams:

{ t: 'App', o: 'Portal' } // Action is left Wild
{ t: 'App' } // Action and Orient are left wild
{} // All 3 Aspects (Term, Action & Orient) are left wild

You can also use empty strings ('') or asterisks (*) to define Wild trigram aspects.

support for asterisks (*) is due to that is a generalized way to describe Wildcard trigrams when describing the software to be written using the TAO

Examples:

{ t: 'App', a: '', o: 'Portal' } // Action is defined Wild
{ t: 'App', a: '*', o: '*' } // Action and Orient are defined wild
{ a: '', o: '*' } // All 3 Aspects are Wild, and the style is mixed

Adding a Wildcard Handler

Adding a Wildcard Handler to the TAO is the same as adding a Concrete Handler to the TAO.

Wildcard Handler for all AppCons on a Term

const handleApp = (tao, data) => {
  console.log(`Look, Ma! We see everything fired on the App! - this one is doing ${tao.a} from ${tao.o}`);
};

TAO.addInlineHandler({ t: 'App' }, handleApp);
// OR
TAO.addInlineHandler({ term: 'App', action: '*', orient: '*' }, handleApp);

Special Note: there is no distinction between the 2 above, the second only includes the other 2 trigram aspects for illustrative purposes.

Wilcard Handler for all AppCons of an Action

const handleViews = (tao, data) => {
  console.log(`Look, Ma! We react to every View! - this one is viewing: ${tao.t} from ${tao.o}`);
};

TAO.addInlineHandler({ a: 'View' }, handleViews);
// OR
TAO.addInlineHandler({ term: '', action: 'View', orient: '' }, handleViews);

Wilcard Handler for all AppCons of an Orient(ation)

const handlePortal = (tao, data) => {
  console.log(`Look, Ma! We react to everything from Portal! - this one is on: ${tao.t} doing ${tao.a}`);
};

TAO.addInlineHandler({ o: 'Portal' }, handlePortal);
// OR
TAO.addInlineHandler({ term: '*', action: '*', orient: 'Portal' }, handlePortal);

Wildcard Handler for ALL AppCons

const handleAll = (tao, data) => {
  console.log(`Look, Ma! We react to everything! - this one is on: ${tao.t} doing ${tao.a} from ${tao.o}`);
};

TAO.addInlineHandler({}, handleAll);
// OR
TAO.addInlineHandler({ term: '*', action: '*', orient: '*' }, handleAll);