1C++11 in Skia
2=============
3
4Skia is exploring the use of C++11.  As a library, we are technically limited
5by what our clients support and what our build bots support.
6
7Skia may also be limited by restrictions we choose put on ourselves.  This
8document is not concerned with C++11 policy in Skia, only its technical
9feasibility.  This is about what we can use, a superset of what we may use.
10
11The gist:
12
13-   C++11 the language as supported by GCC 4.4 or later is probably usable.
14-   If you break a bot, that feature is not usable.
15-   The C++11 standard library can't generally be used.
16-   Local statics are not thread safe.
17
18
19Clients
20-------
21
22The clients we pay most attention to are Chrome, Android, Mozilla, and a few
23internal Google projects.
24
25Chrome builds with a recent Clang on Mac and Linux and with a recent MSVC on
26Windows.  These toolchains are new enough to not be the weak link to use any
27C++11 language feature.  But Chrome still supports Mac OS X 10.6, which does
28not ship with a C++11 standard library.  So [Chrome has banned the use of the
29C++11 standard library](http://chromium-cpp.appspot.com/).  Some header-only
30features are probably technically fine, but the Mac toolchain will prevent us
31from even trying at compile time as long as we target 10.6 as our minimum API
32level.
33
34Chrome intentionally disables thread-safe initialization of static variables,
35and MSVC doesn't support it at all, so we cannot rely on that.
36
37Android builds with either a recent GCC or a recent Clang.  They're generally
38not a weak link for C++11 language features.  Android's C++ standard library
39has always been a pain, but since we can't use it anyway (see Chrome), don't
40worry about it.
41
42Mozilla's current weak link is a minimum requirement of GCC 4.6.  Most features
43marked in red on Mozilla's C++11 [feature
44matrix](https://developer.mozilla.org/en-US/docs/Using_CXX_in_Mozilla_code) are
45marked that way because they arrived in GCC 4.7 or GCC 4.8.  Their
46minimum-supported Clang and MSVC toolchains are great.  They also appear to ban
47the C++ standard library.
48
49Internal Google projects tend to support C++11 completely, including the
50full C++11 standard library.
51
52
53Bots
54----
55
56Most of our bots are pretty up-to-date: the Windows bots use MSVC 2013, the Mac
57bots a recent Clang, and the Linux bots GCC 4.8 or a recent Clang.  Our Android
58bots use a recent toolchain from Android (see above), and our Chrome bots use
59Chrome's toolchains (see above).  I'm not exactly sure what our Chrome OS bots
60are using, but they've never been a problem.
61
62A few miscellaneous compile-only bots are actually our current overall weak link:
63
64-   Our iOS builds are driven from a Mac 10.7 machine using some unknown old Clang.
65    Who knows how old that is or what it supports?  It's probably due for an update.
66
67If we were to eliminate the problems of iOS bots, our ability to
68use C++11 would match Mozilla's list nearly identically.
69