Service.registerService should enforce a service instance implements an interface

[leggetter]

Right now I can register as service as follows:

var br = require( 'br' );
var ServiceRegistry = require( 'br/ServiceRegistry' );

function MyService() {
}

MyService.prototype.doSomething = function() {
  console.log( 'something' );
};

ServiceRegistry.registerService( 'my.something-service', new MyService() );

But the purpose of the ServiceRegistry is (via @james-shaw-turner):

Services are supposed to hide away the implementation details behind a facade and conform to a contract (the interface) This enables us to swap out implementations for tests, workbenches etc. We should add enforcement.

We can do this (enforcement) via Topiarist, but it may need to be updated to expose a way of checking what interfaces a class implements in a more public way. It is possible, it does store a __interfaces__ property right now that we could use.

So, we need to perform a check when a service is registered that that instance provided does implement an interface.

More thought required.

@james-shaw-turner Would you class this as a feature enhancement or a bug?

[james-shaw-turner]

I would say it is an enhancement.
As Adam points out if the service is defined as an alias then this is already covered. We could add checking for the case where services are added programmatically but this shouldn't be common usage. So this is relatively low priority

[janhancic]

Yes, services registered trough aliases are already checked.

But how would you do the checking with registerService? How would you know which interface to check against?