BOOST_PP_REMOVE_PARENS() is dangerously broken -- it strips initial group of parentheses instead of surrounding

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#65 5 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
38/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Quiet
Tech stack
cpp
Domain
compilers

Research direction

Start with the Godbolt reproducer and boost/preprocessor/punctuation/remove_parens.hpp to verify how BOOST_PP_REMOVE_PARENS handles the input. Review the documented contract and determine the intended API change, including compatibility and naming implications. Done means the behavior and documentation agree with an explicitly decided contract, with the reproducer no longer exposing the reported pitfall.

Written by the indexing model from the issue text.

Description

https://godbolt.org/z/38jbTP7qn

#include <boost/preprocessor/punctuation/remove_parens.hpp>

int main(int argc, char *argv[]) {
#if MACRO
  return BOOST_PP_REMOVE_PARENS((*argv)[1]);  // Crash
#else
  return                        (*argv)[1] ;  // OK
#endif
}

Note the documentation piles extra confusion on top of this. It says:

The BOOST_PP_REMOVE_PARENS macro removes the beginning parenthesis, if it exists, from the input data and expands to the result

"Parenthesis" is singular (plural is parentheses), so the documentation is claiming that only a beginning ( is being removed. It makes no mention of removing any closing ), regardless of its expected location, even though the function apparently does that regardless of its location.

This is a massive pitfall. The name BOOST_PP_REMOVE_PARENS itself (and the intended usage) are misleading for most users and very unlikely to be what they actually want.

I would suggest, at the very least, renaming the macro to something like BOOST_PP_REMOVE_BEGINNING_PARENS and updating the documentation to clarify it is not doing what users would expect from a REMOVE_PARENS macro.

Dominant language
C++
Stars
118
Forks
76
PR merge metrics
No merged PRs in 30d

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