https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92687
Bug ID: 92687 Summary: decltype of a structured binding to a tuple component is a reference type inside a template function Product: gcc Version: 9.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: vis...@royal-caliber.com Target Milestone: --- Created attachment 47370 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47370&action=edit preprocessed file Hello, The code below shows an inconsistency in the handling of decltype for structured bindings within template functions vs. non-template functions - the static_assert in foo() triggers, but not in bar(). I think the handling in bar() is correct, as per the notes at https://en.cppreference.com/w/cpp/language/structured_binding. This may or may not be related to bug 81176. Details of the compilation command are listed below the source. Thank you, Vishal ------------------------------------------------------------ #include <type_traits> #include <tuple> template <bool b = false> void foo() { auto [x, y] = std::tuple<int, int>{0, 2}; static_assert(!std::is_reference<decltype(x)>::value); } void bar() { auto [x, y] = std::tuple<int, int>{0, 2}; static_assert(!std::is_reference<decltype(x)>::value); } int main() { foo<>(); bar(); } ----------------------------------------------------------- g++-9.2.0 -v -save-temps -pedantic -Wall -Wextra -std=c++17 test.cpp Using built-in specs. COLLECT_GCC=g++-9.2.0 COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/9.2.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /var/tmp/portage/sys-devel/gcc-9.2.0/work/gcc-9.2.0/configure --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/9.2.0 --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/9.2.0 --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/9.2.0/man --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/9.2.0/info --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include/g++-v9 --with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/9.2.0/python --enable-languages=c,c++,fortran --enable-obsolete --enable-secureplt --disable-werror --with-system-zlib --enable-nls --without-included-gettext --enable-checking=release --with-bugurl=https://bugs.gentoo.org/ --with-pkgversion='Gentoo 9.2.0 p1' --disable-esp --enable-libstdcxx-time --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --disable-multilib --with-multilib-list=m64 --disable-altivec --disable-fixed-point --enable-targets=all --enable-libgomp --disable-libmudflap --disable-libssp --disable-systemtap --enable-vtable-verify --enable-lto --without-isl --enable-default-pie --enable-default-ssp Thread model: posix gcc version 9.2.0 (Gentoo 9.2.0 p1) COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wpedantic' '-Wall' '-Wextra' '-std=c++17' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/libexec/gcc/x86_64-pc-linux-gnu/9.2.0/cc1plus -E -quiet -v -D_GNU_SOURCE test.cpp -mtune=generic -march=x86-64 -std=c++17 -Wpedantic -Wall -Wextra -fpch-preprocess -o test.ii ignoring nonexistent directory "/usr/local/include" ignoring nonexistent directory "/usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/../../../../x86_64-pc-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include/g++-v9 /usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include/g++-v9/x86_64-pc-linux-gnu /usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include/g++-v9/backward /usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include /usr/lib/gcc/x86_64-pc-linux-gnu/9.2.0/include-fixed /usr/include End of search list. COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wpedantic' '-Wall' '-Wextra' '-std=c++17' '-shared-libgcc' '-mtune=generic' '-march=x86-64' /usr/libexec/gcc/x86_64-pc-linux-gnu/9.2.0/cc1plus -fpreprocessed test.ii -quiet -dumpbase test.cpp -mtune=generic -march=x86-64 -auxbase test -Wpedantic -Wall -Wextra -std=c++17 -version -o test.s GNU C++17 (Gentoo 9.2.0 p1) version 9.2.0 (x86_64-pc-linux-gnu) compiled by GNU C version 9.2.0, GMP version 6.1.2, MPFR version 3.1.6, MPC version 1.0.3, isl version none GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 GNU C++17 (Gentoo 9.2.0 p1) version 9.2.0 (x86_64-pc-linux-gnu) compiled by GNU C version 9.2.0, GMP version 6.1.2, MPFR version 3.1.6, MPC version 1.0.3, isl version none GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: 2f11227cf3606c8ecdab2bd17fc2bf18 test.cpp: In function ‘void foo()’: test.cpp:9:17: error: static assertion failed 9 | static_assert(!std::is_reference<decltype(x)>::value); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~