https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125384
Bug ID: 125384
Summary: [c++] this in lambda capture in a member function of a
template class C resolves as C*&, not C*
Product: gcc
Version: 16.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: topin89 at mail dot ru
Target Milestone: ---
Created attachment 64499
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=64499&action=edit
demo code from above with some working variations
Here’s code that works on gcc 15 but not on gcc 16:
template<typename C>
struct At{
void b();
};
template<typename C>
void At<C>::b(){
if constexpr(std::is_same_v<decltype(this), At*>){
std::cout << "decltype(this) == At* \n";
} else if constexpr(std::is_same_v<decltype(this), At*&>){
std::cout << "decltype(this) == At*& \n";
}
[this](){
if constexpr(std::is_same_v<decltype(this), At*>){
std::cout << "decltype(this) == At* \n";
} else if constexpr(std::is_same_v<decltype(this), At*&>){
std::cout << "decltype(this) == At*& \n";
}
static_cast<void>(this);
}();
}
Output should be:
decltype(this) == At*
decltype(this) == At*
But it’s
decltype(this) == At*
decltype(this) == At*&
Output should be:
decltype(this) == At*
decltype(this) == At*
But it’s
decltype(this) == At*
decltype(this) == At*&
If struct is not templated, everything as expected. If you remove
static_cast<void>(this); and make lambda without this captured, everything
works as expected.
attached thisbug.cpp with buggy and correct behavior
gcc version and conf flags is:
LC_ALL=C /opt/gcc16/bin/g++ -v
Using built-in specs.
COLLECT_GCC=/opt/gcc16/bin/g++
COLLECT_LTO_WRAPPER=/opt/gcc16/libexec/gcc/x86_64-pc-linux-gnu/16.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /home/user/gcc16/configure CC=/usr/local/bin/gcc
CXX=/usr/local/bin/g++ --prefix=/opt/gcc16 --enable-languages=c,c++
--disable-multilib --enable-checking=release
--with-build-config='bootstrap-lto-lean bootstrap-O3 bootstrap-native'
--with-pkgversion=gcc-16
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 16.1.0 (gcc-16)
cmdline:
LC_ALL=C /opt/gcc16/bin/g++ thisbug.cpp -o thisbug && ./thisbug
Compiler Explorer link: https://godbolt.org/z/j77xsx8Kv
