Discuss: Allow "input" to update for a workflow in a ContainerViewController/WorkflowHost

[davidapgar]

When rendering a child workflow, the "input" (ie: the Workflow) is updated each time (allowing it to handle an update to its input, via workflowDidChange).

Currently, the root workflow hosted in a WorkflowHost (and ContainerViewController) does not provide any means to update the Workflow - it is just the root workflow, so the outside doesn't have a path to update the input.

We should consider adding this (I believe the Android version does have support for this)

[zach-klippenstein]

We do, our WorkflowHost takes a ReceiveChannel (Signal) of inputs. Super handy because it also lets the first input be provided asynchronously, which turns out to be a pretty common use case given the way our internal integration works.

Here's the change: https://github.com/square/workflow/pull/282/files#diff-c9e75405c1366dc37bf068c0cd37762c