How to pass variables($input) to fields written within getSubscription?

[sidutta]

My components have query fragments of the following form:

initialVariables : {
	type : 'videos',
	pageSize : 10,
	community : 3
},
fragments: {
	viewer: () => Relay.QL`
		fragment on Viewer {
			id,
			newItemsAvailable(type : $type, community : $community),
			newsFeedItems(first : $pageSize, type : $type, community : $community) {
				pageInfo {
					hasNextPage
				},
				edges {
					cursor,
					node {
						...
					}
				}
			}
		}
	`
},

I want to subscribe to changes in the field newItemsAvailable. To do so I would need the following getSubscription function:

getSubscription() {
  return Relay.QL`
    subscription {
      newsFeedItemsAvailableSubscription(input: $input) {
        viewer {
          newItemsAvailable(type : $type, community : $community)
        }
      }
    }
  `;
}

I can't omit (type : $type, community : $community) from here since that would give an error. In the worst case I would have to send dummy hardcoded values.
I guess

subscriptions: [
    ({ viewer, type, community }) => new NewsFeedItemsAvailableSubscription({ viewer, type, community }),
  ]

and

getVariables() {
  return {
    id: this.props.viewer.id,
    type: this.props.type,
    community: this.props.community
  };
}

feed the values of type and community into $input through ...subscription.getVariables(). However, how can I make them available in newItemsAvailable(type : $type, community : $community). I haven't looked into the source code of Relay so have no clue of how all this generally works.

[sidutta]

If the above isn't possible(using data from $input next to subfields), I feel the above snippets are sufficient to get an understanding of what I am trying to do here. What solution do you suggest? ${input.type} gives an error(Error: You supplied a GraphQL document that uses template substitution for an argument value, but variable substitution has not been enabled.) too. Does Relay store fields fetched using separate variables separately? If so, I think it makes sense to subscribe multiple times on the same field using different variables.

[sidutta]

Since subscriptions are based on mutations, facebook/relay#1046 seems relevant. Especially the comment by nodkz on the "new Mutation API".