Implement constructor manually due to GCC issues

Question

(This is not a duplicate of another question since in the other one the question is about the compilation issue (where somebody suggested to implement a constructor), and here there is an specific question about how to implement that constructor manually)

In order to compile the following program with GCC 4.9.2, It has to be modified. I have to implement the constructor manually and I dont know how to do it.

The line 6 is causing trouble and is the one that needs to be modified: 'TabStats::TabStats(TabStats&& other) noexcept = default;'

As a condition, the no-except specifier cant be removed.

SOURCE CODE:

#include "browser/resource_coordinator/tab_stats.h"
#include "build/build_config.h"    
namespace resource_coordinator {
TabStats::TabStats() = default;
TabStats::TabStats(const TabStats& other) = default;
TabStats::TabStats(TabStats&& other) noexcept = default;
TabStats::~TabStats() {}
TabStats& TabStats::operator=(const TabStats& other) = default;
}  // namespace resource_coordinator

tab_stats.h is included below:

#ifndef BROWSER_RESOURCE_COORDINATOR_TAB_STATS_H_
#define BROWSER_RESOURCE_COORDINATOR_TAB_STATS_H_
#include <stdint.h>
#include <vector>
#include "base/process/process.h"
#include "base/strings/string16.h"
#include "base/time/time.h"
#include "build/build_config.h"

namespace content {
class RenderProcessHost;
}  // namespace content

namespace resource_coordinator {

struct TabStats {
  TabStats();
  TabStats(const TabStats& other);
  TabStats(TabStats&& other) noexcept;
  ~TabStats();

  TabStats& operator=(const TabStats& other);

  bool is_app = false;            // Browser window is an app.
  bool is_internal_page = false;  // Internal page, such as NTP or Settings.
  // Playing audio, accessing cam/mic or mirroring display.
  bool is_media = false;
  bool is_pinned = false;
  bool is_in_visible_window = false;
  bool is_in_active_window = false;
  // Whether this is the active tab in a browser window.
  bool is_active = false;
  bool is_discarded = false;
  // User has entered text in a form.
  bool has_form_entry = false;
  int discard_count = 0;
  bool has_beforeunload_handler = false;
  base::TimeTicks last_active;
  base::TimeTicks last_hidden;
  content::RenderProcessHost* render_process_host = nullptr;
  base::ProcessHandle renderer_handle = 0;
  int child_process_host_id = 0;
  base::string16 title;
#if defined(OS_CHROMEOS)
  int oom_score = 0;
#endif
  int64_t tab_contents_id = 0;  // Unique ID per WebContents.
  bool is_auto_discardable = true;
};

typedef std::vector<TabStats> TabStatsList;

}  // namespace resource_coordinator

#endif  // BROWSER_RESOURCE_COORDINATOR_TAB_STATS_H_

This is the compilation error Im getting (I removed many flags to make this shorter):

[20689/29018] CXX obj/chrome/browser/browser/tab_stats.o
FAILED: obj/chrome/browser/browser/tab_stats.o 
g++ -MMD -MF obj/chrome/browser/browser/tab_stats.o.d -DUSE_LIBSECRET -DV8_DEPRECATION_WARNINGS -DUSE_UDEV -DUSE_AURA=1 -DUSE_PANGO=1 -DUSE_CAIRO=1 -DUSE_GLIB=1 -DUSE_NSS_CERTS=1 -DUSE_X11=1 -DNO_TCMALLOC -DDISABLE_NACL -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D_FORTIFY_SOURCE=2 -DNDEBUG -DUSE_CUPS -DUSE_GNOME_KEYRING -DGLIB_VERSION_MAX_ALLOWED=GLIB_VERSION_2_32 -DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_26 -DUSE_GLX -DSK_SUPPORT_GPU=1 -DV8_USE_EXTERNAL_STARTUP_DATA -DWEBRTC_CHROMIUM_BUILD -DWEBRTC_POSIX -DWEBRTC_LINUX -DHUNSPELL_STATIC --param=ssp-buffer-size=4 -fstack-protector -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -funwind-tables -fPIC -pipe -pthread -m32 -msse2 -mfpmath=sse -mmmx -Wall -O2 -g0 -fvisibility=hidden -DLIBXML_STATIC= -std=gnu++11 -nostdinc++ -isystem../../buildtools/third_party/libc++/trunk/include -isystem../../buildtools/third_party/libc++abi/trunk/include -Wno-narrowing -fno-rtti -fno-exceptions -fvisibility-inlines-hidden -c ../../chrome/browser/resource_coordinator/tab_stats.cc -o obj/chrome/browser/browser/tab_stats.o
../../chrome/browser/resource_coordinator/tab_stats.cc:14:1: error: function 'resource_coordinator::TabStats::TabStats(resource_coordinator::TabStats&&)' defaulted on its redeclaration with an exception-specification that differs from the implicit declaration 'resource_coordinator::TabStats::TabStats(resource_coordinator::TabStats&&)'
 TabStats::TabStats(TabStats&& other) noexcept = default;

 ^

Answer 1

There are only two cases when you should have to write your own move constructor, and both of them make little sense:

• when one of the base classes does not have move semantics, but then having move semantics for your derived class does not make sense at all.
• when one of your class data member does not have move semantics, but then having move semantics for your class does not quite make sense.

Usually this would involve replacing the move operation by a copy.

A good starting point for writing your own move constructor, is to do what the the compiler does:

• Call the move constructors of base classes (You must use std::move).
• Call the move contructor of all class members. (use std::move).

ex:

struct A {};  // must have a move constructor, be it a default or not.

struct B : A
{
    B(B&& b) 
        : A(std::move(b))
        , data1_(std::move(b.data1_))
        , data2_(std::move(b.data2_))
    {}

    some_type        data1_;
    some_other_type  data2_;
};

Nothing exciting here, which is why the default works in most cases. Classes that cannot be moved are pretty rare.