Compositional Initialization

@Joe_Groff wrote:

Having a way to assemble a value from a collection of keypath-value pairs would be interesting, I agree. I think that belongs in the same general bucket of reflection mechanisms as things like StoredPropertyIterable .

You're right, that proposal is definitely in the same "reflection" bucket. My playground implementation linked above relies on the reflection features from Swift 4, but having some enhanced capabilities like those mentioned in StoredPropertyIterable would be great.