vctrs 0.2.2

• New vec_as_subscript() function to cast inputs to the base type
  of a subscript (logical, numeric, or character). vec_as_index()
  has been renamed to vec_as_location(). Use num_as_location() if
  you need more options to control how numeric subscripts are
  converted to a vector of locations.

• New vec_as_subscript2(), vec_as_location2(), and
  num_as_location2() variants for validating scalar subscripts and
  locations (e.g. for indexing with [[).

• vec_as_location() now preserves names of its inputs if possible.

• vec_ptype2() methods for base classes now prevent
  inheritance. This makes sense because the subtyping graph created by
  vec_ptype2() methods is generally not the same as the inheritance
  relationships defined by S3 classes. For instance, subclasses are
  often a richer type than their superclasses, and should often be
  declared as supertypes (e.g. vec_ptype2() should return the
  subclass).

  We introduced this breaking change in a patch release because
  new_vctr() now adds the base type to the class vector by default,
  which caused vec_ptype2() to dispatch erroneously to the methods
  for base types. We'll finish switching to this approach in vctrs
  0.3.0 for the rest of the base S3 classes (dates, data frames, ...).

• vec_equal_na() now works with complex vectors.

• vctrs_vctr class gains an as.POSIXlt() method (#717).

• vec_is() now ignores names and row names (#707).

• vec_slice() now support Altvec vectors (@jimhester, #696).

• vec_proxy_equal() is now applied recursively across the columns of
  data frames (#641).

• vec_split() no longer returns the val column as a list_of. It is now
  returned as a bare list (#660).

• Complex numbers are now coercible with integer and double (#564).

• zeallot has been moved from Imports to Suggests, meaning that %<-% is no
  longer re-exported from vctrs.

• vec_equal() no longer propagates missing values when comparing list
  elements. This means that vec_equal(list(NULL), list(NULL)) will continue to
  return NA because NULL is the missing element for a list, but now
  vec_equal(list(NA), list(NA)) returns TRUE because the NA values are
  compared directly without checking for missingness.

• Lists of expressions are now supported in vec_equal() and functions that
  compare elements, such as vec_unique() and vec_match(). This ensures that
  they work with the result of modeling functions like glm() and mgcv::gam()
  which store "family" objects containing expressions (#643).

• new_vctr() gains an experimental inherit_base_type argument
  which determines whether or not the class of the underlying type
  will be included in the class.

• list_of() now inherits explicitly from "list" (#593).

• vec_ptype() has relaxed default behaviour for base types; now if two
  vectors both inherit from (e.g.) "character", the common type is also
  "character" (#497).

• vec_equal() now correctly treats NULL as the missing value element for
  lists (#653).

• vec_cast() now casts data frames to lists rowwise, i.e. to a list of
  data frames of size 1. This preserves the invariant of
  vec_size(vec_cast(x, to)) == vec_size(x) (#639).

• Positive and negative 0 are now considered equivalent by all functions that
  check for equality or uniqueness (#637).

• New experimental functions vec_group_rle() for returning run
  length encoded groups; vec_group_id() for constructing group
  identifiers from a vector; vec_group_loc() for computing the
  locations of unique groups in a vector (#514).

• New vec_chop() for repeatedly slicing a vector. It efficiently captures
  the pattern of map(indices, vec_slice, x = x).

• Support for multiple character encodings has been added to functions that
  compare elements within a single vector, such as vec_unique(), and across
  multiple vectors, such as vec_match(). When multiple encodings are
  encountered, a translation to UTF-8 is performed before any comparisons are
  made (#600, #553).

• Equality and ordering methods are now implemented for raw and
  complex vectors (@romainfrancois).