Live Collections

Traditional programs (like those in Rust) typically manipulate collections of data elements, such as those stored in a Vec or HashMap. These collections are fixed in the sense that any transformations applied to them such as map are immediately executed on a snapshot of the collection. This means that the output will not be updated when the input collection is modified.

In Hydro, programs instead work with live collections which are expected to dynamically change over time as new elements are added or removed (in response to API requests, streaming ingestion, etc). Applying a transformation like map to a live collection results in another live collection that will dynamically change over time.