Patch the infinite recursion of asJSON on subclasses of vctrs_vctr instances…

[coissac]

Goals of the PR

To answer what I expect to be a better way to #424, I propose the following patch, which changes the asJSON method for the vcrts::vctrs_vctr class.

Principle of the patch

The idea of this patch is to allow people who develop classes derived from the vcrts::vctrs_vctr class to add an S3 method called vec_proxy_json to their class. This follows the same principle implemented in the vctrs package for the comparison operators and ordering operations involving subclasses of vctrs_vctr (i.e., the vec_proxy_compare and vec_proxy_order methods). The method must change the original vector into a new one that can be easily converted into JSON (e.g. a simple character, integer, numeric, or logical vector), or into something more sophisticated if needed, such as a list.

A version of the vec_proxy_json method is implemented for the original vctrs_vctr class. It mimics the original asJSON code for the vcrts::vctrs_vctr class.

Effect of the patch

According to the exchange in issue #424, the bug was introduced as a workaround for issue #408. I have reproduced the example with the patch applied to test if it works as expected.

loadNamespace("posterior") # (>= 1.3.0)
# <environment: namespace:posterior>

x <- structure("a", class = c("vctrs_vctr", "character"))

jsonlite:::asJSON(x)
# [1] "[\"a\"]"

If you create two simple instances of vctrs_vctr, one wrapping an integer vector, the second wrapping a character vector, both will produce the correct json.

z <- vctrs::new_vctr(1:10)

z
# <vctrs_vctr[10]>
#  [1]  1  2  3  4  5  6  7  8  9 10

jsonlite:::asJSON(z)
# [1] "[1,2,3,4,5,6,7,8,9,10]"

zc <- vctrs::new_vctr(as.character(1:10))  

jsonlite:::asJSON(zc)
# [1] "[\"1\",\"2\",\"3\",\"4\",\"5\",\"6\",\"7\",\"8\",\"9\",\"10\"]"

Hopping that it can help.

All the best

Eric