Supports treating a linear sequence of resources as a single resource.

A Hotswap[F, R] instance is created as a Resource and hence, has a lifetime that is scoped by the Resource. After creation, a Resource[F, R] can be swapped in to the Hotswap by calling swap. The acquired resource is returned and is finalized when the Hotswap is finalized or upon the next call to swap, whichever occurs first.

For example, the sequence of three resources r1, r2, r3 are shown in the following diagram:

>----- swap(r1) ---- swap(r2) ---- swap(r3) ----X
|        |             |             |          |
Creation |             |             |          |
        r1 acquired    |             |          |
                      r2 acquired    |          |
                      r1 released   r3 acquired |
                                    r2 released |
                                               r3 released

This class is particularly useful when working with pulls that cycle through resources -- e.g., writing bytes to files, rotating files every N bytes or M seconds. Without Hotswap, such pulls leak resources -- on each file rotation, a file handle or at least an internal resource reference accumulates. With Hotswap, the Hotswap instance is the only registered resource and each file is swapped in to the Hotswap.

Usage typically looks something like:

Stream.resource(Hotswap(mkResource)).flatMap { case (hotswap, r) =>
  // Use r, call hotswap.swap(mkResource) as necessary
}

See fs2.io.file.writeRotate for an example of usage.