https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100157
Bug ID: 100157
Summary: Support `__type_pack_element` like Clang
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: vittorio.romeo at outlook dot com
Target Milestone: ---
Clang provides a `__type_pack_element` builtin which allows efficient indexing
of parameter packs in variadic templates, and it seems that GCC has no
equivalent.
This forces users interested in minimizing compilation times to resort to
arcane implemenations such as these ones:
https://github.com/kvasir-io/mpl/blob/development/src/kvasir/mpl/sequence/lookup.hpp
A builtin like `__type_pack_element` would not only allow user code to compile
faster, but also anything inside libstdc++ that needs to index a type list
(e.g. `std::tuple_element_t`) would benefit from it.
This is the Clang test driver, to show an usage example:
https://github.com/llvm-mirror/clang/blob/master/test/SemaCXX/type_pack_element.cpp
This is the Clang pull request:
https://reviews.llvm.org/D15421
