问为什么这段涉及std::tuple隐式构造的代码在c++11/14模式下编译？
EN

Stack Overflow用户

提问于 2017-01-27 14:12:34

回答 1查看 160关注 0票数 5

根据http://en.cppreference.com/w/cpp/utility/tuple/tuple的说法，std::tuple不能在C++17之前隐式构造。他们甚至给出了一个例子来演示它：

std::tuple<int, int> foo_tuple() 
{
  return {1, -1};  // Error until C++17
  return std::make_tuple(1, -1); // Always works
}

然而，使用gcc 6.2和clang 3.8.1，我可以在C++11和C++14模式下干净地编译这段代码：

piotrek@piotrek-Inspiron-5423:~/test$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/6/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 6.2.0-5ubuntu12' --with-bugurl=file:///usr/share/doc/gcc-6/README.Bugs --enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-6 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-6-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-6-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-6-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 6.2.0 20161005 (Ubuntu 6.2.0-5ubuntu12) 
piotrek@piotrek-Inspiron-5423:~/test$ clang++ -v
clang version 3.8.1-12ubuntu1 (tags/RELEASE_381/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/i686-linux-gnu/6.2.0
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/5.4.1
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/6.2.0
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/6.2.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.4.1
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.2.0
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/6.2.0
Candidate multilib: .;@m64
Selected multilib: .;@m64
piotrek@piotrek-Inspiron-5423:~/test$ cat test.cpp 
#include <tuple>

std::tuple<int, int> f()
{
    return {1,1};
}
piotrek@piotrek-Inspiron-5423:~/test$ clang++ -Wall -pedantic -fsyntax-only -std=c++14 test.cpp 
piotrek@piotrek-Inspiron-5423:~/test$ clang++ -Wall -pedantic -fsyntax-only -std=c++11 test.cpp 
piotrek@piotrek-Inspiron-5423:~/test$ g++ -Wall -pedantic -fsyntax-only -std=c++14 test.cpp 
piotrek@piotrek-Inspiron-5423:~/test$ g++ -Wall -pedantic -fsyntax-only -std=c++11 test.cpp 
piotrek@piotrek-Inspiron-5423:~/test$