https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96917
Bug ID: 96917
Summary: decltype(auto) variable initialized with lambda
by-reference capture has incorrect type
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: andrey.vihrov at gmail dot com
Target Milestone: ---
Consider
#include <type_traits>
int main()
{
int x = 5;
[&]() {
decltype(auto) b = x;
static_assert(std::is_same<decltype(b), int>::value, "types should
match");
};
}
When compiled simply with "g++ x.cpp", this gives
x.cpp: In lambda function:
x.cpp:9:59: error: static assertion failed: types should match
9 | static_assert(std::is_same<decltype(b), int>::value, "types
should match");
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
Note that replacing decltype(auto) with decltype(x) fixes the error. Clang
accepts both assertions.
Although it is not specified explicitly, from
http://eel.is/c++draft/expr.prim.lambda.capture it may seem that the variable
captured by reference has the original type and not the reference type inside
the lambda. Please correct me if this is wrong.
gcc -v:
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/10.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure --prefix=/usr --libdir=/usr/lib
--libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++,d --with-isl
--with-linker-hash-style=gnu --with-system-zlib --enable-__cxa_atexit
--enable-cet=auto --enable-checking=release --enable-clocale=gnu
--enable-default-pie --enable-default-ssp --enable-gnu-indirect-function
--enable-gnu-unique-object --enable-install-libiberty --enable-linker-build-id
--enable-lto --enable-multilib --enable-plugin --enable-shared
--enable-threads=posix --disable-libssp --disable-libstdcxx-pch
--disable-libunwind-exceptions --disable-werror
gdc_include_dir=/usr/include/dlang/gdc
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.2.0 (GCC)
