[vtk-developers] Request for a gentler tone in commit message verbiage...

[Robert Maynard]

It has to be 2012 or newer as this is a noted break in functionality
between C++98 and C++11 ( and forward ).

Here is the excerpt on what has changed:
"

Following a breaking change between the C++98/03 and C++11 standards,
using explicit template arguments to call make_pair()—as in
make_pair<int, int>(x, y)—typically does not compile in Visual C++ in
Visual Studio 2012. The solution is to always call make_pair() without
explicit template arguments—as in make_pair(x, y). Providing explicit
template arguments defeats the purpose of the function. If you require
precise control over the resulting type, use pair instead
of make_pair—as in pair<short, short>(int1, int2).


Another breaking change between the C++98/03 and C++11 standards: When
A is implicitly convertible to B and B is implicitly convertible to C,
but A is not implicitly convertible to C, C++98/03 and Visual C++ 2010
permitted pair<A, X> to be converted (implicitly or explicitly) to
pair<C, X>. (The other type, X, is not of interest here, and this is
not specific to the first type in the pair.) Because C++11 and Visual
C++ in Visual Studio 2012 detect that A is not implicitly convertible
to C, they remove the pair conversion from overload resolution. This
is a positive change for many scenarios. For example, overloading
func(const pair<int, int>&) and func(const pair<string, string>&), and
calling func() with pair<const char *, const char *> will compile with
this change. However, this change breaks code that relied on
aggressive pair conversions. Such code can typically be fixed by
performing one part of the conversion explicitly—for example, by
passing make_pair(static_cast<B>(a), x) to a function that expects
pair<C, X>.

"
The reason that we haven't seen this with other compilers is either
they haven't enabled C++11 (with c++11 standard library) or they
compile options are lax and allow this behavior. This is the challenge
of supporting Visual Studio 2010 and forward, they only compile with
C++11 enabled which causes these very subtle issues.

Note because we require C++98 support we can't use the approach that
Visual Studio recommends

article: https://msdn.microsoft.com/en-us/library/vstudio/bb531344%28v=vs.110%29.aspx

On Wed, Apr 29, 2015 at 3:54 PM, David Lonie <david.lonie at kitware.com> wrote:
> On Wed, Apr 29, 2015 at 3:44 PM, Sean McBride <sean at rogue-research.com>
> wrote:
>>
>> On Wed, 29 Apr 2015 13:50:53 -0400, David Cole via vtk-developers said:
>>
>> >claims there was some sort of problem with make_pair and double. What
>> >exactly was the problem? With what exact version of MSVC? (I don't buy
>> >that there's a general problem with make_pair and double...)
>>
>> I'll steer clear of the larger point... :)  but will just say: when adding
>> workarounds for problematic compilers / OSes, it would be very appreciated
>> to be clear about which versions.  As someone who has gone through VTK to
>> expunge obsolete workarounds, it's sometimes been hard to know what's
>> obsolete and what's not.  A lot of workaround notes say things like "on
>> Apple this is broken", but which OS version is not stated...
>>
>> Try to think of the future in commit messages and code comments.  :)
>
>
> +1. In this case, the workaround is still valid code, no alternate paths,
> and just a slight change in syntax, so we won't have to worry about removing
> it in the future :D I did leave a note in-line warning future maintainers
> that the line is troublesome for MSVC and should be treated with caution.
>
> I am somewhat curious what version of the compiler this was too, I can't
> really tell from the CDash page:
>
> https://open.cdash.org/viewBuildError.php?buildid=3784595
>
> IIRC, we used to have this prominently displayed in the build name. Looks
> like that got dropped somewhere along the way. I'll see if we can get that
> info back in.
>
> Dave
>
>
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