Package: g++-11
Version: 11.2.0-19
Severity: normal
Contrary to clang++, g++ does not honor "friend" statement when evaluating
template specialization
Here is a short example:
$ cat toto6.cpp
#include <iostream>
struct X {
template <class T, class U = void> struct check_is_map {
static constexpr bool value = false;
};
template <class T>
struct check_is_map<T, typename T::is_map> {
static constexpr bool value = true;
};
};
template <class T, class U = void> struct check_is_map {
static constexpr bool value = false;
};
template <class T>
struct check_is_map<T, typename T::is_map> {
static constexpr bool value = true;
};
struct Config {
using is_map=void;
};
struct ConfigBis {
private:
template <typename T1, typename U1>
friend struct check_is_map; // friend of the template
friend struct X; // friend of the surrounding class
using is_map=void;
};
int main()
{
std::cerr << "VALUE (public): "
<< check_is_map<Config>::value
<< std::endl;
std::cerr << "VALUE (private+friend): "
<< check_is_map<ConfigBis>::value
<< std::endl;
std::cerr << "X::VALUE (public): "
<< X::check_is_map<Config>::value
<< std::endl;
std::cerr << "X::VALUE (private+friend): "
<< X::check_is_map<ConfigBis>::value
<< std::endl;
}
$ clang++ -std=gnu++17 -Wall -Wextra toto6.cpp
$ ./a.out
VALUE (public): 1
VALUE (private+friend): 1
X::VALUE (public): 1
X::VALUE (private+friend): 1
$ g++ -std=gnu++17 -Wall -Wextra toto6.cpp
$ ./a.out
VALUE (public): 1
VALUE (private+friend): 0
X::VALUE (public): 1
X::VALUE (private+friend): 0
Regards,
Vincent
-- System Information:
Debian Release: bookworm/sid
APT prefers stable-updates
APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500,
'oldstable-updates'), (500, 'unstable'), (500, 'testing'), (500, 'stable'),
(500, 'oldstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386, armel, mipsel
Kernel: Linux 5.16.0-6-amd64 (SMP w/4 CPU threads; PREEMPT)
Kernel taint flags: TAINT_OOT_MODULE
Locale: LANG=fr_FR.utf8, LC_CTYPE=fr_FR.utf8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages g++-11 depends on:
ii gcc-11 11.2.0-19
ii gcc-11-base 11.2.0-19
ii libc6 2.33-7
ii libgmp10 2:6.2.1+dfsg-3
ii libisl23 0.24-2
ii libmpc3 1.2.1-2
ii libmpfr6 4.1.0-3
ii libstdc++-11-dev 11.2.0-19
ii libzstd1 1.4.10+dfsg-1
ii zlib1g 1:1.2.11.dfsg-4
g++-11 recommends no packages.
Versions of packages g++-11 suggests:
pn g++-11-multilib <none>
ii gcc-11-doc 11.2.0-1
-- no debconf information
