mardi 31 mars 2015

ternary operator of different types

The following piece of code behaves differently under g++ 4.9.2 and clang++ 3.7.0. Which one is correct? What part in standard is related to this? Thanks.



#include <iostream>
using namespace std;

struct Base {
Base() = default;
Base(const Base&) = default;
Base(Base&&) = delete;
};

struct Derived : Base {
};

int main() {
const Base& b = true ? Derived() : Base();
}


g++ accepts it and clang++ gives an error incompatible operand types ('Derived' and 'Base'). See below for details.



[hidden]$ g++ -v
Using built-in specs.
COLLECT_GCC=/usr/bin/g++
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.9.2/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://ift.tt/1fOljwq --enable-bootstrap --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-linker-hash-style=gnu --enable-languages=c,c++,objc,obj-c++,fortran,ada,go,lto --enable-plugin --enable-initfini-array --disable-libgcj --with-isl=/builddir/build/BUILD/gcc-4.9.2-20150212/obj-x86_64-redhat-linux/isl-install --with-cloog=/builddir/build/BUILD/gcc-4.9.2-20150212/obj-x86_64-redhat-linux/cloog-install --enable-gnu-indirect-function --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.9.2 20150212 (Red Hat 4.9.2-6) (GCC)
[hidden]$ g++ -std=c++11 b.cpp
[hidden]$ clang++ -v
clang version 3.7.0 (http://ift.tt/1n0Utol 6bbdbba8ec8a7730c68fee94363547dc2dc65b10)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/3.4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.9.2
Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.9.2
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
[hidden]$ clang++ -std=c++11 b.cpp
b.cpp:14:24: error: incompatible operand types ('Derived' and 'Base')
const Base& b = true ? Derived() : Base();
^ ~~~~~~~~~ ~~~~~~
1 error generated.

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