Support nullable `external_ptr<>`

Open

#312 opened on Apr 2, 2023 1 comment 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 3/5
Estimated time: 1-2 days
Newbie friendliness: 35/100

Issue type: Feature
Clarity: Mostly clear
Activity status: Stale
Tech stack: cpp, r
Domain: api

Research direction

Read cpp11/external_pointer.hpp and start with the external_pointer cases exercised by the cpp_source examples. Reproduce both nullptr and R_NilValue inputs in R; done means the chosen nullable behavior is consistent in both directions and existing external-pointer behavior remains valid.

Written by the indexing model from the issue text.

Description

Currently, a nullptr but not an R_NilValue can be assigned to an external_ptr<> object. This is inconsistent and surprising, in particular because the roundtrip works correctly the other way. Should we support this?

CC @hannes @TMonster.

library(cpp11)

# Works
cpp_source(
  code = '
  #include "cpp11/external_pointer.hpp"
  #include "cpp11/strings.hpp"

  [[cpp11::register]]
  cpp11::external_pointer<int> test() {
    return cpp11::external_pointer<int>(nullptr);
  }
  '
)

test()
#> NULL

# Fails, but perhaps shouldn't
cpp_source(
  code = '
  #include "cpp11/external_pointer.hpp"
  #include "cpp11/strings.hpp"

  [[cpp11::register]]
  cpp11::external_pointer<int> test() {
    return cpp11::external_pointer<int>(R_NilValue);
  }
  '
)

test()
#> Error: Invalid input type, expected 'externalptr' actual 'NULL'

^{Created on 2023-04-02 with reprex v2.0.2}

Dominant language: C++
Stars: 224
Forks: 52
PR merge metrics: No merged PRs in 30d

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