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Should the default `SEXP` in `r_vector` be a typed vector of length 0 rather than `R_NilValue`?

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#392 0 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
35/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
cpp, r
Domain
backend

Research direction

Start at r_vector's default construction and data_ handling, then inspect how default-constructed vectors currently behave when attributes are assigned. Evaluate the proposed typed, length-zero SEXP against the allocation and noexcept trade-offs, and validate that default construction supports attributes without requiring R_NilValue handling.

Written by the indexing model from the issue text.

Description

i.e. to support things like https://github.com/r-lib/cpp11/issues/315 where you default construct the vector and immediately try and put attributes on it.

Would also simplify internal code that currently has to account for the possibility of R_NilValue as data_ quite a bit.

We'd have to write our own default constructor but I think that's totally possible?


A downside of this is that the default constructor would have to allocate and would no longer be noexcept or as "cheap", but I can't see that mattering much because you eventually allocate anyways?

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

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