vctrs 0.3.3

• The table class is now implemented as a wrapper type that
  delegates its coercion methods. It used to be restricted to integer
  tables (#1190).

• Named one-dimensional arrays now behave consistently with simple
  vectors in vec_names() and vec_rbind().

• new_rcrd() now uses df_list() to validate the fields. This makes
  it more flexible as the fields can now be of any type supported by
  vctrs, including data frames.

• Thanks to the previous change the [[ method of records now
  preserves list fields (#1205).

• vec_data() now preserves data frames. This is consistent with the
  notion that data frames are a primitive vector type in vctrs. This
  shouldn't affect code that uses [[ and length() to manipulate
  the data. On the other hand, the vctrs primitives like vec_slice()
  will now operate rowwise when vec_data() returns a data frame.

• outer is now passed unrecycled to name specifications. Instead,
  the return value is recycled (#1099).

• Name specifications can now return NULL. The names vector will
  only be allocated if the spec function returns non-NULL during the
  concatenation. This makes it possible to ignore outer names without
  having to create an empty names vector when there are no inner
  names:

  zap_outer_spec <- function(outer, inner) if (is_character(inner)) inner
  
  # `NULL` names rather than a vector of ""
  names(vec_c(a = 1:2, .name_spec = zap_outer_spec))
  #> NULL
  
  # Names are allocated when inner names exist
  names(vec_c(a = 1:2, c(b = 3L), .name_spec = zap_outer_spec))
  #> [1] ""  ""  "b"
  

• Fixed several performance issues in vec_c() and vec_unchop()
  with named vectors.

• The restriction that S3 lists must have a list-based proxy to be considered
  lists by vec_is_list() has been removed (#1208).

• New performant data_frame() constructor for creating data frames in a way
  that follows tidyverse semantics. Among other things, inputs are recycled
  using tidyverse recycling rules, strings are never converted to factors,
  list-columns are easier to create, and unnamed data frame input is
  automatically spliced.

• New df_list() for safely and consistently constructing the data structure
  underlying a data frame, a named list of equal-length vectors. It is useful
  in combination with new_data_frame() for creating user-friendly
  constructors for data frame subclasses that use the tidyverse rules for
  recycling and determining types.

• Fixed performance issue with vec_order() on classed vectors which
  affected dplyr::group_by() (tidyverse/dplyr#5423).

• vec_set_names() no longer alters the input in-place (#1194).

• New vec_proxy_order() that provides an ordering proxy for use in
  vec_order() and vec_sort(). The default method falls through to
  vec_proxy_compare(). Lists are special cased, and return an integer
  vector proxy that orders by first appearance.

• List columns in data frames are no longer comparable through vec_compare().

• The experimental relax argument has been removed from
  vec_proxy_compare().