if_else() coerces NA as list(NULL) when the false argument is a list

[arnaudgallou]

See this example:

dplyr::if_else(
  TRUE,
  NA,
  list("foo")
)
#> [[1]]
#> NULL

dplyr::if_else(
  TRUE,
  NA,
  "foo"
)
#> [1] NA

^{Created on 2024-08-27 with reprex v2.1.0}

Is this the desired behavior? I'd expect if_else() to return list(NA) in the first case.

[arnaudgallou]

In the end, that might be the desired behavior but maybe that could be mentioned in if_else() (and possibly in vctrs::vec_cast_common()) that NA will be changed to NULL in that case.

[DavisVaughan]

It is expected behavior. The "missing" type for a list is list(NULL), so NA is cast to that when we compute the common type.

There's really no good place to put docs for this, as it is quite specific and not that common, but I'll add an example to vec_init() with a list to show that the NA element for a list is NULL