Give list_all_vectors() and list_check_all_vectors() ptype and size arguments?

[DavisVaughan]

Because sometimes you want to check that a list is homogeneous in its type, or that all elements are the same size

tidyverse/dplyr#6300 (comment)
tidyverse/dplyr#6300 (comment)

The ptype arg might be a little tricky, because vec_assert(ptype =) is a little hard to formalize, and would need to be translated to C

[DavisVaughan]

Or maybe we should implement list_all_size(x, size)

This would error if any element of x isn't a vector, but otherwise returns TRUE or FALSE. I feel like having it separated from the vector check would be useful, and it is faster than all(list_sizes(x) == 1L)

[DavisVaughan]

Also useful here tidyverse/purrr#935

[DavisVaughan]

I think we have decided to implement:

• list_all_size()
• list_check_all_size()
  Since we already have list_sizes(), and this is a small wrapper around that to make it faster

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The ptype check is a little strange, because do you really want list_check_all_vector(.ptype = double()) to enforce that all elements of the list are double? Or do you want them to be castable to double? Typically you just use vec_cast_common() here instead.