furrr 0.2.0

Breaking changes:

• All furrr functions now enforce tidyverse recycling rules (for example,
  between .x and .y in future_map2()). Previously this was mostly the
  case, except with size zero input. Recycling between input of size 0 and
  input of size >1 no longer recycles to size 0, and is instead an error.
  purrr will begin to do this as well in the next major release (#134).

• future_options() has been deprecated in favor of furrr_options().
  Calling future_options() will still work, but will trigger a once per
  session warning and will eventually be removed. This change was made to
  free up this function name in case the future package ever wants to use it.

• In a future version of furrr, the .progress argument will be deprecated
  and removed in favor of the
  progressr
  package. The progress bar has not yet been removed in furrr 0.2.0, however
  I would encourage you to please start using progressr if possible. It uses
  a much more robust idea, and has been integrated with future
  in such a way that it can relay near real-time progress updates from
  sequential, multisession, and even cluster futures (meaning that remote
  connections can return live updates). Multicore support will come at some
  point as well. That said, be aware that it is a relatively new package
  and the API is still stabilizing. As more people use it, its place in the
  future ecosystem will become clearer, and tighter integration with furrr
  will likely be possible.

Features / Fixes:

• New pkgdown article
  on using furrr with progressr
  for generating progress updates.

• New pkgdown article
  discussing an alternative strategy to automatic globals detection using
  the carrier package.

• New pkgdown article
  discussing how furrr "chunks" input to send if off to workers.

• New pkgdown article
  on common gotchas when using furrr.

• New pkgdown article
  detailing how to use furrr with remote AWS EC2 connections.

• future_walk() and friends have been added to mirror purrr::walk().

• furrr_options() now has a variety of new arguments for fine tuning furrr.
  These are based on advancements made in both future and future.apply. The
  most important is chunk_size, which can be used as an alternative
  to scheduling to determine how to break up .x into chunks to send off
  to the workers. See ?furrr_options for full details.

• future_pmap() and its variants now propagate the names of the first element
  of .l onto the output (#116).

• future_pmap() and its variants now work with empty list() input (#135).

• future_modify(), future_modify_if() and future_modify_at() have been
  brought up to date with the changes in purrr 0.3.0 to their non-parallel
  equivalents. Specifically, they now wrap [[<- and return the same type
  as the input when the input is an atomic vector (#119).

• future_map_if() and future_modify_if() gained the .else argument that
  was added to purrr's map_if() and modify_if() in purrr 0.3.0 (#132).

• All *_raw() variants from purrr have been added, such as
  future_map_raw() (#122).

• All furrr functions gained a new argument, .env_globals, which determines
  the environment in which globals for .x and ... are
  looked up. It defaults to the caller environment, which is different than
  what was previously used, but should be more correct in some edge cases.
  Most of the time, you should not have to touch this argument. Additionally,
  globals for .f are now looked up in the function environment of .f
  (futureverse/future.apply#62, #153).

• The future specific global option future.globals.maxSize now scales with
  the number of elements of .x that get exported to each worker. This
  helps prevent some false positives about exporting objects that are too large,
  and is the same approach taken in future.apply (#113).

• .x is now searched for globals. Only globals found in the slice of .x
  that corresponds to worker X are exported to worker X. This is relevant if
  .x is, say, a list of functions where each has their own set of globals
  (#16).

• The progress bar furrr creates now outputs to stderr rather than stdout.

• The progress bar is now only enabled for multisession, multicore, and
  multiprocess strategies. It has never worked for sequential futures or
  cluster futures using remote connections, but .progress is now forced
  to false in those cases.

• future_invoke_map() and its variants have been marked as retired to match
  purrr::invoke_map().

• The internals of furrr have been overhauled to unify the implementations of
  future_map(), future_map2(), future_pmap() and all of their variants.
  This should make furrr much easier to maintain going forward (#44).

• A MIT license is now used.

Version requirements:

• rlang >= 0.3.0 is now required to ensure that the rlang ~ is serializable.
  The hacks in furrr that tried to work around this have been removed (#123).

• future >= 1.19.1 is now required to be able to use future::value() instead
  of the soon to be deprecated future::values() and to access a few bug
  fixes (#108).

• purrr >= 0.3.0 is now required to gain access to various new features and
  breaking changes. For example, map_if() gained an .else argument, which
  has been added to future_map_if().

• globals >= 0.13.1 is now required because of substantial new speed boosts
  there related to searching for global variables, and to gain access to a few
  bug fixes.