remove template c++11'ism in Heap.h

remove template c++11'ism in Heap.h

Followup to CL 486193002 to remove default arguments from template types,
which is only allowed in c++11 and later (and we haven't officially switched
to c++11 yet afaik).

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=181719

[Mostyn Bramley-Moore, 2014-09-10 00:16:21]

mostynb@opera.com changed reviewers:
+ ager@chromium.org, haraken@chromium.org, wibling@chromium.org,
zerny@chromium.org

[Mostyn Bramley-Moore, 2014-09-10 00:17:11]

@haraken, wibling, mads, zerny: please take a look...

[haraken, 2014-09-10 00:51:03]

What's the benefit of this change?

[haraken, 2014-09-10 00:51:10]

https://codereview.chromium.org/559733004/diff/1/Source/platform/heap/Heap.h
File Source/platform/heap/Heap.h (right):

https://codereview.chromium.org/559733004/diff/1/Source/platform/heap/Heap.h#...
Source/platform/heap/Heap.h:1107: // TODO(mostynb) remove this once c++11 is
allowed, in favour of the one

TODO(mostynb) => FIXME

https://codereview.chromium.org/559733004/diff/1/Source/platform/heap/Heap.h#...
Source/platform/heap/Heap.h:1580: // TODO(mostynb) remove this once c++11 is
allowed, in favour of the one above:

Ditto.

[Mads Ager (chromium), 2014-09-10 06:36:30]

I would prefer not to add code duplication if this does not break compilation on
any of our supported systems (which as far as I can tell it doesn't).

[Mads Ager (chromium), 2014-09-10 06:48:10]

Default template arguments are not a c++11 feature as far as I know? Template
parameter pack arguments are a c++11 feature, but that is not what we are using
here.

http://en.cppreference.com/w/cpp/language/template_parameters

Default template arguments are used in many places in Blink. In particular they
are used heavily in WTF collection and here in the GC infrastructure.

[Mostyn Bramley-Moore, 2014-09-10 08:02:25]

mostynb@opera.com changed reviewers:
+ thakis@chromium.org

[Mostyn Bramley-Moore, 2014-09-10 08:09:16]

On 2014/09/10 00:51:03, haraken wrote:
> What's the benefit of this change?

This allows this code to build on non-c++11 toolchains a little longer.

Last I heard from Nico on chromium-dev was that we're supposed to hold off on
c++11 a little longer.  I can keep this as a local patch while migrating all my
toolchains/targets to gcc >= 4.8, but I guess Nico has some reasons for wanting
to hold back on c++11 for you guys too.

On 2014/09/10 06:48:10, Mads Ager (chromium) wrote:
> I would prefer not to add code duplication if this does not break compilation
on
> any of our supported systems (which as far as I can tell it doesn't).

Removed the duplication in patchset 2, making this quite a bit simpler.

> Default template arguments are not a c++11 feature as far as I know? Template
> parameter pack arguments are a c++11 feature, but that is not what we are
using
> here.
> 
> http://en.cppreference.com/w/cpp/language/template_parameters
> 
> Default template arguments are used in many places in Blink. In particular
they
> are used heavily in WTF collection and here in the GC infrastructure.

I'm not sure why this hasn't been a problem elsewhere, but GCC's documentation
lists this as a c++11 feature, see the "Default template arguments for function
templates" entry:
https://gcc.gnu.org/projects/cxx0x.html

This is the error I get when building without this patch (my local tree, so the
line numbers might differ) with ubuntu 14.04's g++-4.6:

In file included from
../../third_party/WebKit/Source/platform/heap/Handle.h:34:0,
                 from
../../third_party/WebKit/public/platform/WebPrivatePtr.h:37,
                 from
../../third_party/WebKit/public/platform/WebPrerender.h:35,
                 from ../../third_party/WebKit/Source/platform/Prerender.cpp:36:
../../third_party/WebKit/Source/platform/heap/Heap.h:1088:97: error: default
template arguments may not be used in function templates without -std=c++0x or
-std=gnu++0x

If I sub in g++-4.7 in the build command, without rerunning gyp, I get the same
error except it uses the term c++11 and gnu++11 instead.  (If I rerun gyp then
-std=gnu++11 is used for gcc >= 4.7).

https://codereview.chromium.org/559733004/diff/1/Source/platform/heap/Heap.h
File Source/platform/heap/Heap.h (right):

https://codereview.chromium.org/559733004/diff/1/Source/platform/heap/Heap.h#...
Source/platform/heap/Heap.h:1107: // TODO(mostynb) remove this once c++11 is
allowed, in favour of the one
On 2014/09/10 00:51:10, haraken wrote:
> 
> TODO(mostynb) => FIXME

Done.

https://codereview.chromium.org/559733004/diff/1/Source/platform/heap/Heap.h#...
Source/platform/heap/Heap.h:1580: // TODO(mostynb) remove this once c++11 is
allowed, in favour of the one above:
On 2014/09/10 00:51:10, haraken wrote:
> 
> Ditto.

Done.

[Mads Ager (chromium), 2014-09-10 08:19:03]

LGTM

Sorry about that; I was thinking about default template arguments for classes
which has been available forever. Thanks for the simplification! :)

[Mostyn Bramley-Moore, 2014-09-10 08:21:21]

The CQ bit was checked by mostynb@opera.com

[commit-bot: I haz the power, 2014-09-10 08:21:26]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mostynb@opera.com/559733004/20001

[haraken, 2014-09-10 08:28:40]

LGTM

[commit-bot: I haz the power, 2014-09-10 09:29:12]

Committed patchset #2 (id:20001) as 181719