Allow GCC 4.9 to compile Chromium

Allow GCC 4.9 to compile Chromium

In order to implicit cast an lvalue to an rvalue when returning
from a function, the return type and type of variable in the return
statement previously had to be exactly the same. When this was not
the case, std::move was required. For instance, when returning a
std::unique_ptr<Derived> variable in a function with a
std::unique_ptr<Base> return type, std::move is required.

DR 1579 changed this, and allows for implicitly converting
to the return type, if the return type has a constructor(T&&), where
T is the type of the local variable being returned. DR 1579 was
implemented in GCC 5, but not in GCC 4.9 and below. By explicitly
qualifying the local variable with std::move, we allow for compiling
with GCC 4.9 and incur no performance penalty. The code is still
absolutely correct to the word of C++11.

BUG=chromium:682965
See also:
* https://bugs.gentoo.org/show_bug.cgi?id=600288
* https://stackoverflow.com/questions/22018115/converting-stdunique-ptrderived-to-stdunique-ptrbase#comment33375875_22018521
* http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3833.html#1579

Review-Url: https://codereview.webrtc.org/2642053003
Cr-Commit-Position: refs/heads/master@{#16175}
Committed: https://chromium.googlesource.com/external/webrtc/+/888874f761fdd69bb9448b3905627289b5fd66dd

[Mike Gilbert, 2017-01-19 21:22:07]

Description was changed from

==========
Allow GCC 4.9 to compile Chromium

In order to implicit cast an lvalue to an rvalue when returning
from a function, the return type and type of variable in the return
statement previously had to be exactly the same. When this was not
the case, std::move was required. For instance, when returning a
std::unique_ptr<Derived> variable in a function with a
std::unique_ptr<Base> return type, std::move is required.

DR 1579 changed this, and allows for implicitly converting
to the return type, if the return type has a constructor(T&&), where
T is the type of the local variable being returned. DR 1579 was
implemented in GCC 5, but not in GCC 4.9 and below. By explicitly
qualifying the local variable with std::move, we allow for compiling
with GCC 4.9 and incur no performance penalty. The code is still
absolutely correct to the word of C++11.

See also:
* https://bugs.gentoo.org/show_bug.cgi?id=600288
*
https://stackoverflow.com/questions/22018115/converting-stdunique-ptrderived-...
* http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3833.html#1579
==========

to

==========
Allow GCC 4.9 to compile Chromium

In order to implicit cast an lvalue to an rvalue when returning
from a function, the return type and type of variable in the return
statement previously had to be exactly the same. When this was not
the case, std::move was required. For instance, when returning a
std::unique_ptr<Derived> variable in a function with a
std::unique_ptr<Base> return type, std::move is required.

DR 1579 changed this, and allows for implicitly converting
to the return type, if the return type has a constructor(T&&), where
T is the type of the local variable being returned. DR 1579 was
implemented in GCC 5, but not in GCC 4.9 and below. By explicitly
qualifying the local variable with std::move, we allow for compiling
with GCC 4.9 and incur no performance penalty. The code is still
absolutely correct to the word of C++11.

See also:
* https://bugs.gentoo.org/show_bug.cgi?id=600288
*
https://stackoverflow.com/questions/22018115/converting-stdunique-ptrderived-...
* http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3833.html#1579
==========

[Mike Gilbert, 2017-01-19 21:22:08]

floppymaster@gmail.com changed reviewers:
+ alexeypa@chromium.org, jiayl@webrtc.org, sergeyu@chromium.org,
wez@chromium.org

[Mike Gilbert, 2017-01-19 21:22:32]

Please have a look. Thanks!

[Mike Gilbert, 2017-01-19 21:22:44]

floppymaster@gmail.com changed reviewers:
- alexeypa@chromium.org

[Sergey Ulanov, 2017-01-19 22:16:53]

lgtm

[Mike Gilbert, 2017-01-19 23:32:40]

The CQ bit was checked by floppymaster@gmail.com

[commit-bot: I haz the power, 2017-01-19 23:32:47]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.webrtc.org/...

[commit-bot: I haz the power, 2017-01-19 23:37:57]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-01-19 23:37:58]

Try jobs failed on following builders:
  presubmit on master.tryserver.webrtc (JOB_FAILED,
http://build.chromium.org/p/tryserver.webrtc/builders/presubmit/builds/12458)

[Mike Gilbert, 2017-01-20 03:08:16]

Description was changed from

==========
Allow GCC 4.9 to compile Chromium

In order to implicit cast an lvalue to an rvalue when returning
from a function, the return type and type of variable in the return
statement previously had to be exactly the same. When this was not
the case, std::move was required. For instance, when returning a
std::unique_ptr<Derived> variable in a function with a
std::unique_ptr<Base> return type, std::move is required.

DR 1579 changed this, and allows for implicitly converting
to the return type, if the return type has a constructor(T&&), where
T is the type of the local variable being returned. DR 1579 was
implemented in GCC 5, but not in GCC 4.9 and below. By explicitly
qualifying the local variable with std::move, we allow for compiling
with GCC 4.9 and incur no performance penalty. The code is still
absolutely correct to the word of C++11.

See also:
* https://bugs.gentoo.org/show_bug.cgi?id=600288
*
https://stackoverflow.com/questions/22018115/converting-stdunique-ptrderived-...
* http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3833.html#1579
==========

to

==========
Allow GCC 4.9 to compile Chromium

In order to implicit cast an lvalue to an rvalue when returning
from a function, the return type and type of variable in the return
statement previously had to be exactly the same. When this was not
the case, std::move was required. For instance, when returning a
std::unique_ptr<Derived> variable in a function with a
std::unique_ptr<Base> return type, std::move is required.

DR 1579 changed this, and allows for implicitly converting
to the return type, if the return type has a constructor(T&&), where
T is the type of the local variable being returned. DR 1579 was
implemented in GCC 5, but not in GCC 4.9 and below. By explicitly
qualifying the local variable with std::move, we allow for compiling
with GCC 4.9 and incur no performance penalty. The code is still
absolutely correct to the word of C++11.

BUG=chromium:682965

See also:
* https://bugs.gentoo.org/show_bug.cgi?id=600288
*
https://stackoverflow.com/questions/22018115/converting-stdunique-ptrderived-...
* http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3833.html#1579
==========

[Mike Gilbert, 2017-01-20 03:08:32]

Description was changed from

==========
Allow GCC 4.9 to compile Chromium

In order to implicit cast an lvalue to an rvalue when returning
from a function, the return type and type of variable in the return
statement previously had to be exactly the same. When this was not
the case, std::move was required. For instance, when returning a
std::unique_ptr<Derived> variable in a function with a
std::unique_ptr<Base> return type, std::move is required.

DR 1579 changed this, and allows for implicitly converting
to the return type, if the return type has a constructor(T&&), where
T is the type of the local variable being returned. DR 1579 was
implemented in GCC 5, but not in GCC 4.9 and below. By explicitly
qualifying the local variable with std::move, we allow for compiling
with GCC 4.9 and incur no performance penalty. The code is still
absolutely correct to the word of C++11.

BUG=chromium:682965

See also:
* https://bugs.gentoo.org/show_bug.cgi?id=600288
*
https://stackoverflow.com/questions/22018115/converting-stdunique-ptrderived-...
* http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3833.html#1579
==========

to

==========
Allow GCC 4.9 to compile Chromium

In order to implicit cast an lvalue to an rvalue when returning
from a function, the return type and type of variable in the return
statement previously had to be exactly the same. When this was not
the case, std::move was required. For instance, when returning a
std::unique_ptr<Derived> variable in a function with a
std::unique_ptr<Base> return type, std::move is required.

DR 1579 changed this, and allows for implicitly converting
to the return type, if the return type has a constructor(T&&), where
T is the type of the local variable being returned. DR 1579 was
implemented in GCC 5, but not in GCC 4.9 and below. By explicitly
qualifying the local variable with std::move, we allow for compiling
with GCC 4.9 and incur no performance penalty. The code is still
absolutely correct to the word of C++11.

BUG=chromium:682965


See also:
* https://bugs.gentoo.org/show_bug.cgi?id=600288
*
https://stackoverflow.com/questions/22018115/converting-stdunique-ptrderived-...
* http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3833.html#1579
==========

[Mike Gilbert, 2017-01-20 03:08:42]

The CQ bit was checked by floppymaster@gmail.com

[commit-bot: I haz the power, 2017-01-20 03:08:45]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.webrtc.org/...

[commit-bot: I haz the power, 2017-01-20 04:20:45]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1484881722084750, "parent_rev":
"8944ab3fec59dbc7c281cf919c6aea1befe2c94a", "commit_rev":
"888874f761fdd69bb9448b3905627289b5fd66dd"}

[commit-bot: I haz the power, 2017-01-20 04:20:48]

Description was changed from

==========
Allow GCC 4.9 to compile Chromium

In order to implicit cast an lvalue to an rvalue when returning
from a function, the return type and type of variable in the return
statement previously had to be exactly the same. When this was not
the case, std::move was required. For instance, when returning a
std::unique_ptr<Derived> variable in a function with a
std::unique_ptr<Base> return type, std::move is required.

DR 1579 changed this, and allows for implicitly converting
to the return type, if the return type has a constructor(T&&), where
T is the type of the local variable being returned. DR 1579 was
implemented in GCC 5, but not in GCC 4.9 and below. By explicitly
qualifying the local variable with std::move, we allow for compiling
with GCC 4.9 and incur no performance penalty. The code is still
absolutely correct to the word of C++11.

BUG=chromium:682965


See also:
* https://bugs.gentoo.org/show_bug.cgi?id=600288
*
https://stackoverflow.com/questions/22018115/converting-stdunique-ptrderived-...
* http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3833.html#1579
==========

to

==========
Allow GCC 4.9 to compile Chromium

In order to implicit cast an lvalue to an rvalue when returning
from a function, the return type and type of variable in the return
statement previously had to be exactly the same. When this was not
the case, std::move was required. For instance, when returning a
std::unique_ptr<Derived> variable in a function with a
std::unique_ptr<Base> return type, std::move is required.

DR 1579 changed this, and allows for implicitly converting
to the return type, if the return type has a constructor(T&&), where
T is the type of the local variable being returned. DR 1579 was
implemented in GCC 5, but not in GCC 4.9 and below. By explicitly
qualifying the local variable with std::move, we allow for compiling
with GCC 4.9 and incur no performance penalty. The code is still
absolutely correct to the word of C++11.

BUG=chromium:682965


See also:
* https://bugs.gentoo.org/show_bug.cgi?id=600288
*
https://stackoverflow.com/questions/22018115/converting-stdunique-ptrderived-...
* http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3833.html#1579

Review-Url: https://codereview.webrtc.org/2642053003
Cr-Commit-Position: refs/heads/master@{#16175}
Committed:
https://chromium.googlesource.com/external/webrtc/+/888874f761fdd69bb9448b390...
==========

[commit-bot: I haz the power, 2017-01-20 04:20:49]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/external/webrtc/+/888874f761fdd69bb9448b390...