Re: Updated draft list

ram@zedat.fu-berlin.de (Stefan Ram) wrote or quoted:

2025-03-15   N5008    N5001     C++26

  C++26

  C++26 is shaping up to be a substantial update, introducing several
  highly anticipated features and language improvements.

  For the language, it adds contracts, introducing language-level
  support for design by contract, allowing specification of
  preconditions, postconditions, and invariants for functions
  and methods.

  It brings static reflection capabilities, enabling compile-time
  introspection of types and program structure, a major addition
  for advanced metaprogramming and tooling.

  It enables constexpr cast from void*, making certain generic
  programming techniques possible at compile time.

  User-generated static_assert messages are now allowed, improving
  diagnostics in template-heavy code.

  Placeholder variables with no name are permitted, simplifying
  code that requires unused variables.

  Pack indexing enhances template parameter pack manipulation.

  Attributes can now be applied to structured bindings.

  There are improved diagnostics and safety for uninitialized variable
  reads.

  Functions can be deleted with a custom reason string.

  Variadic friends are enabled.

  Constexpr placement new extends constant evaluation to placement
  new expressions.

  Structured binding declaration as a condition is now possible.

  There are clarifications to template constraint resolution.

  Deleting a pointer to an incomplete type is now ill-formed,
  strengthening type safety.

  Structured bindings can introduce a pack.

  Exception throwing in constant-evaluation is permitted.

  There is more flexibility in constant expressions involving
  structured bindings and references to constexpr variables.

  The Oxford variadic comma deprecates ellipsis parameters without
  a preceding comma for better C compatibility.

  Deprecated array comparisons are removed.

  In the standard library, C++26 adds hashing for std::chrono
  value classes, a std::is_within_lifetime utility, native
  handles in file streams, string and bitset interoperability with
  std::string_view, expanded constexpr support for <cmath> and
  <complex>, and 2022 SI prefixes for ratios such as std::quecto,
  std::ronto, std::ronna, and std::quetta.

  It introduces std::copyable_function, a more flexible function
  wrapper, and std::submdspan() for enhanced multidimensional
  span operations.

  There is a new <debugging> header for standard debugging support and
  a <linalg> header introducing a BLAS-like linear algebra interface.

  The tuple protocol is extended to std::complex.

  The ranges library gains views::concat for concatenating ranges,
  string and string view concatenation, std::ranges::generate_random
  for random number generation over ranges, and the ability
  to print blank lines with std::println().

  There is a std::formatter for std::filesystem::path and
  saturation arithmetic functions like std::add_sat and
  std::div_sat for safe arithmetic.

  Other notable changes include the removal of deprecated
  atomic initialization APIs such as atomic_init and
  ATOMIC_VAR_INIT, standardization of BLAS-like operations and
  SIMD parallelism, and various proposals to improve safety,
  including those championed by Bjarne Stroustrup.

  Some features are still under discussion or not yet finalized,
  such as further expansion of reflection, continued work
  on concepts lite for template constraints, and further
  integration of the Ranges v3 library.

  C++23

  C++23 is a moderate update compared to C++20, focusing on incremental
  improvements to both the core language and the standard library.

  In the core language, it introduces explicit object parameters
  (deducing this), if consteval for compile-time branching,
  multidimensional subscript operators, built-in decay copy
  support, marking unreachable code, platform-independent
  assumptions, and named universal character escapes.

  In the standard library, it brings string formatting
  improvements including formatting entire ranges, standard named
  modules (std and std.compat), new containers like flat_map and
  flat_set, multidimensional span (mdspan), a standard generator
  coroutine, monadic operations on std::optional, runtime
  stacktrace support, many improvements to the ranges library,
  and std::expected as an alternative to exceptions.