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From: "john.lindgren at aol dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/66501] New: Default move assignment does not move array members
Date: Thu, 11 Jun 2015 06:48:00 -0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 5.1.0
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X-Bugzilla-Who: john.lindgren at aol dot com
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66501

            Bug ID: 66501
           Summary: Default move assignment does not move array members
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: john.lindgren at aol dot com
  Target Milestone: ---

In the following code, main() should return 0 (and did with GCC 4.8.2).  With
GCC 5.1.0, main() instead returns 2.  It seems that the compiler-generated
Container::operator=(Container&&) does not call Object::operator=(Object&&) as
it ought.  So the line "container=Container()" line does not subtract 2 from
total_size as would be expected.

int total_size;

struct Object
{
    int size = 0;

    Object () = default;

    ~Object () {
        total_size -= size;
    }

    Object (const Object &) = delete;
    Object & operator= (const Object &) = delete;

    Object (Object && b) {
        size = b.size;
        b.size = 0;
    }

    Object & operator= (Object && b) {
        if (this != & b) {
            total_size -= size;
            size = b.size;
            b.size = 0;
        }
        return * this;
    }

    void grow () {
        size ++;
        total_size ++;
    }
};

struct Container {
    Object objects[2];
};

int main (void)
{
    Container container;

    // grow some objects in the container
    for (auto & object : container.objects)
        object.grow ();

    // now empty it
    container = Container ();

    return total_size;
}

gcc -v gives:

Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/5.1.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /build/gcc-multilib/src/gcc-5-20150519/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++ --enable-shared
--enable-threads=posix --enable-libmpx --with-system-zlib --with-isl
--enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu
--disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object
--enable-linker-build-id --enable-lto --enable-plugin
--enable-install-libiberty --with-linker-hash-style=gnu
--enable-gnu-indirect-function --enable-multilib --disable-werror
--enable-checking=release --with-default-libstdcxx-abi=c++98
Thread model: posix
gcc version 5.1.0 (GCC)