type-list-of.md
In vctrs: Vector Helpers

print method gives human friendly output

Code
  list_of(1, 2:3)
Output
  <list_of<double>[2]>
  [[1]]
  [1] 1

  [[2]]
  [1] 2 3

Code
  tibble::tibble(x = list_of(1, 2:3))
Output
  # A tibble: 2 x 1
              x
    <list<dbl>>
  1         [1]
  2         [2]

str method is reasonably correct

Code
  str(x)
Output
  list<dbl> [1:2] 
  $ : num 1
  $ : num [1:2] 2 3
  @ ptype: num(0)

Code
  str(list(list(x, y = 2:1)))
Output
  List of 1
   $ :List of 2
    ..$  : list<dbl> [1:2] 
    .. ..$ : num 1
    .. ..$ : num [1:2] 2 3
    .. ..@ ptype: num(0) 
    ..$ y: int [1:2] 2 1

Code
  str(x[0])
Output
  list<dbl> [1:0] 
   list()
  @ ptype: num(0)

Code
  str(list(list(x[0], y = 2:1)))
Output
  List of 1
   $ :List of 2
    ..$  : list<dbl> [1:0] 
   list()
    .. ..@ ptype: num(0) 
    ..$ y: int [1:2] 2 1

list coercions are symmetric and unchanging

Code
  print(mat)
Output
                     list   list_of<integer>   list_of<double>   list_of<character>  
  list               "list" "list"             "list"            "list"              
  list_of<integer>   "list" "list_of<integer>" "list_of<double>" "list"              
  list_of<double>    "list" "list_of<double>"  "list_of<double>" "list"              
  list_of<character> "list" "list"             "list"            "list_of<character>"

error call is passed to inner cast methods

Code
  (expect_error(fn1()))
Output
  <error/vctrs_error_cast>
  Error in `fn1()`:
  ! Can't convert `..1` <double> to <character>.
Code
  (expect_error(fn2()))
Output
  <error/vctrs_error_cast>
  Error in `fn2()`:
  ! Can't convert `..1` <double> to <character>.