Feature request: Promise-based API for singleton services.

[bolinfest]

Because services are basically the only way to communicate between Atom packages, it is common that there is expected to be exactly one provider for a given service. As such, it would be convenient if there were a Promise-based API to subscribe to the first provider registered for a service in a given range:

var promise = global.services.consumeOnly('special-build-toolbar', '1.0.0');

If there are multiple providers for special-build-toolbar at the time consumeOnly is called, then it could return a Promise that rejects.

[thomasjo]

At first glance I'm 👍 on this feature request. Seems like it could reduce boilerplate code.

How would you handle the rejection gracefully?

try {
  var promise = global.services.consumeOnly('special-build-toolbar', '1.0.0');
} catch (error) {
  // ?
}

I'm sure as the package ecosystem continues to grow, we'll run into scenarios with multiple providers, so I think it's worth having a story for handling that within your suggested scheme.

[bolinfest]

Here's what I'm doing right now:

'use babel';
/* @flow */

function consumeFirstProvider(keyPath: string, version = '0.0.0'): Promise {
  return new Promise((resolve, reject) => {
    var sub = atom.packages.serviceHub.consume(keyPath, version, provider => {
      resolve(provider);
      sub.dispose();
    });
  });
}

module.exports = {
  consumeFirstProvider,
};

In this implementation, the returned Promise may never resolve, but it will never reject.