• Fixed an issue where cpp11::stop() and cpp11::warning() calls with the same template instantiation could cause a crash on some systems (#491, #295).

• cpp_source() now works with multiple files (#492).

• Removed non-API usage of R_NamespaceRegistry.

• Fixed a bug with CPP11_USE_FMT where the input was not being correctly wrapped in fmt::runtime().

• Removed non-API usage of ATTRIB() (#481).

• Improved hygiene around using C++ specific C compatibility headers (i.e. by using <cstring> rather than <string.h> and <cstddef> rather than <stddef.h>) (#454, @MichaelChirico).

• Fixed an rchk issue related to std::initializer_list<named_arg> (#457, @pachadotdev).

• Fixed an issue related to -Wdeprecated-literal-operator (#447, @andrjohns).

• cpp11 now requires R >=4.0.0, in line with the
  tidyverse version policy (#411).

• Because cpp11 now requires R >=4.0.0, a number of previously optional tools
  are now always available, allowing us to remove some dead code. In
  particular:

  • R_UnwindProtect() is always available, so the defines HAS_UNWIND_PROTECT
    and CPP11_UNWIND are no longer useful.

  • ALTREP is always available, so the file cpp11/altrep.hpp and the define
    HAS_ALTREP are no longer useful.

  We would like to remove the dead code regarding these tools in the future, so
  we ask that you please remove usage of them from your own packages (#411).

• R_NO_REMAP and STRICT_R_HEADERS are now conditionally defined only if they
  have not already been defined elsewhere. This is motivated by the fact that
  R_NO_REMAP is becoming the default for C++ code in R 4.5.0 (#410).

• Fixed a small protection issue flagged by rchk (#408).

R non-API related changes

• Removed usage of the following R non-API functions:

  • SETLENGTH()

  • SET_TRUELENGTH()

  • SET_GROWABLE_BIT()

  These functions were used as part of the efficient growable vectors that
  cpp11 offered, i.e. what happens under the hood when you use push_back().
  The removal of these non-API functions means that cpp11 writable vectors that
  have been pushed to with push_back() will likely force 1 extra allocation
  when the conversion from cpp11::writable::r_vector<T> to SEXP occurs
  (typically when you return a result back to R). This does not affect the
  performance of push_back() itself, and in general these growable vectors
  are still quite efficient (#362).

• The environment class no longer uses the non-API function
  Rf_findVarInFrame3() (#367).

  • The exists() method now uses the new R_existsVarInFrame() function.

  • The SEXP conversion operator now uses the new R_getVar() function. Note
    that this is stricter than Rf_findVarInFrame3() in 3 ways. The object
    must exist in the environment (i.e. R_UnboundValue is no longer returned),
    the object cannot be R_MissingArg, and if the object was a promise, that
    promise is now evaluated. We have backported this new strictness to older
    versions of R as well.

New features

• cpp11::writable::r_vector<T>::proxy now implements copy assignment.
  Practically this means that x[i] = y[i] now works when both x and y
  are writable vectors (#300, #339).

• New writable::data_frame constructor that also takes the number of rows as
  input. This accounts for the edge case where the input list has 0 columns but
  you'd still like to specify a known number of rows (#272).

• std::max_element() can now be used with writable vectors (#334).

• Read only r_vectors now have a move constructor and move assignment
  operator (#365).

Improvements and fixes

• Repeated assignment to a cpp11::writable::strings vector through either
  x[i] = elt or x.push_back(elt) is now more performant, at the tradeoff
  of slightly less safety (as long as elt is actually a CHARSXP and i is
  within bounds, there is no chance of failure, which are the same kind of
  invariants placed on the other vector types) (#378).

• Constructors for writable vectors from initializer_list<named_arg> now
  check that named_arg contains a length 1 object of the correct type, and
  throws either a cpp11::type_error or std::length_error if that is not the
  case (#382).

• cpp11::package now errors if given a package name that hasn't been loaded
  yet. Previously it would cause R to hang indefinitely (#317).

• cpp11::function now protects its underlying function, for maximum safety
  (#294).

• cpp11::writable::r_vector<T>::iterator no longer implicitly deletes its
  copy assignment operator (#360).

• Added the missing implementation for x.at("name") for read only vectors
  (#370).

• Fixed an issue with the writable::matrix copy constructor where the
  underlying SEXP should have been copied but was not. It is now consistent with
  the behavior of the equivalent writable::r_vector copy constructor.

• Fixed a memory leak with the cpp11::writable::r_vector move assignment
  operator (#338).

• Fixed an issue where writable vectors were being protected twice (#365).

• The approach for the protection list managed by cpp11 has been tweaked
  slightly. In 0.4.6, we changed to an approach that creates one protection list
  per compilation unit, but we now believe we've found an approach that is
  guaranteed by the C++ standard to create one protection list per package,
  which makes slightly more sense and still has all the benefits of the reduced
  maintanence burden mentioned in the 0.4.6 news bullet (#364).

  A side effect of this new approach is that the preserved object exposed
  through protect.hpp no longer exists. We don't believe that anyone was using
  this. This also means you should no longer see "unused variable" warnings
  about preserved (#249).

Breaking changes

• R >=3.6.0 is now required. This is in line with (and even goes beyond) the
  tidyverse standard of supporting the previous 5 minor releases of R.

• Implicit conversion from sexp to bool, size_t, and double has been
  marked as deprecated and will be removed in the next version of cpp11. The 3
  packages that were using this have been notified and sent PRs. The recommended
  approach is to instead use cpp11::as_cpp<T>, which performs type and length
  checking, making it much safer to use.

• Dropped support for gcc 4.8, mainly an issue for extremely old CentOS 7
  systems which used that as their default compiler. As of June 2024, CentOS 7
  is past its vendor end of support date and therefore also out of scope for
  Posit at this time (#359).

• Internal changes requested by CRAN to fix invalid format string tokens
  (@paleolimbot, #345).

• R >=3.5.0 is now required to use cpp11. This is in line with (and even goes
  beyond) the tidyverse standard of supporting the previous 5 minor releases of
  R. It also ensures that R_UnwindProtect() is available to avoid C++ memory
  leaks (#332).

• cpp11::preserved.release_all() has been removed. This was intended to
  support expert developers on R <3.5.0 when cpp11 used a global protection
  list. Since cpp11 no longer uses a global protection list and requires R

  =3.5.0, it is no longer needed. As far as we can tell, no package was
  actively using this (#332).

• cpp11 now creates one protection list per compilation unit, rather than one
  global protection list shared across compilation units and across packages.
  This greatly reduces the complexity of managing the protection list state and
  should make it easier to make changes to the protection list structure in the
  future without breaking packages compiled with older versions of cpp11 (#330).

• Nested calls to cpp11::unwind_protect() are no longer supported or
  encouraged. Previously, this was something that could be done for performance
  improvements, but ultimately this feature has proven to cause more problems
  than it is worth and is very hard to use safely. For more information, see the
  new vignette("FAQ") section titled "Should I call cpp11::unwind_protect()
  manually?" (#327).

• The features and bug fixes from cpp11 0.4.4 have been added back in.

• On 2023-07-20, cpp11 was temporarily rolled back to 0.4.3 manually by CRAN due
  to a bug in 0.4.4 which we could not immediately fix due to the cpp11
  maintainer being on vacation.

• Davis Vaughan is now the maintainer.

• as_doubles() and as_integers() now propagate missing values correctly
  (#265, #319).

• Fixed a performance issue related to nested unwind_protect() calls (#298).

• Minor performance improvements to the cpp11 protect code. (@kevinushey)

• Silenced an unknown attribute warning specific to the Intel compiler
  (r-lib/systemfonts#98).

• cpp_register() gains an argument extension= governing the file extension of
  the src/cpp11 file. By default it's .cpp, but .cc is now supported
  as well (#292, @MichaelChirico)