[boost] enabling constexpr with Visual studio 2015 Update 3 (RC)

[Paul A. Bristow]

I am trying to use the enhanced constexpr features and have (perhaps unwisely) downloaded the latest Visual Studio Update 3 (RC) to
get as great a chance of achieving this as possible.

https://blogs.msdn.microsoft.com/vcblog/2015/12/02/constexpr-in-vs2015-update-1/ (and later posts)

I am unsure what I need to do to ensure that the compiler is enabled for use the latest features.

I have added /std:c++14 to the options of the property for the project.

(aside I also tried /std:C++latest but that works for some tasks but failed to compile with odd-looking errors in converter.hpp

Error C2518 keyword 'typename' illegal in base class list; ignored
\modular-boost\boost\numeric\conversion\detail\converter.hpp 453

// Trivial Converter : used when (cv-unqualified) T == (cv-unqualified) S
//
template<class Traits>
struct trivial_converter_impl : public std::unary_function< BOOST_DEDUCED_TYPENAME Traits::argument_type
,BOOST_DEDUCED_TYPENAME Traits::result_type
>
,public dummy_range_checker<Traits>
{...}

So I stopped trying that /std:c++latest option. What else should it do?)

Running the modular-boost/libs/config/config_info.cpp program

BOOST_NO_CXX14_CONSTEXPR [no value]

BOOST_CONSTEXPR [no value]
BOOST_CONSTEXPR_OR_CONST =const
BOOST_STATIC_CONSTEXPR =static const

These don't seem to be what I think that I would expect (constexpr and static constexpr).

I want especially to use BOOST_STATIC_CONSTEXPR to get static constexpr.

Do I need to also add #define BOOST_CXX14_CONSTEXPR in my program or elsewhere?
(Doing this doesn't change BOOST_CONSTEXPR_OR_CONST from const to constexpr)

Thanks for any suggestions.

Paul

---
Paul A. Bristow
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+44 (0) 1539 561830




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[Glen Fernandes]

On Sat, Jun 11, 2016 at 11:41 AM, Paul A. Bristow wrote:
> Do I need to also add #define BOOST_CXX14_CONSTEXPR in my program or elsewhere?
> (Doing this doesn't change BOOST_CONSTEXPR_OR_CONST from const to constexpr)
>

In develop, you have the option of defining BOOST_MSVC_CXX11_CONSTEXPR.

Glen

[Marcel Raad]

pabristow wrote

> (aside I also tried /std:C++latest but that works for some tasks but
> failed to compile with odd-looking errors in converter.hpp
>
> Error C2518 keyword 'typename' illegal in base class list; ignored
> \modular-boost\boost\numeric\conversion\detail\converter.hpp 453
>
> // Trivial Converter : used when (cv-unqualified) T == (cv-unqualified) S
> //
> template
> <class Traits>
> struct trivial_converter_impl : public std::unary_function<
> BOOST_DEDUCED_TYPENAME Traits::argument_type
>
> ,BOOST_DEDUCED_TYPENAME Traits::result_type
> >
> ,public dummy_range_checker
> <Traits>
> {...}
>
> So I stopped trying that /std:c++latest option. What else should it do?)

To use /std:C++latest, you have to add _HAS_AUTO_PTR_ETC=1 to the
preprocessor definitions. Otherwise, there is no std::unary_function.



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Sent from the Boost - Dev mailing list archive at Nabble.com.

[Beman Dawes]

On Sat, Jun 11, 2016 at 11:57 AM, Glen Fernandes <glen.fe...@gmail.com>
wrote:

> On Sat, Jun 11, 2016 at 11:41 AM, Paul A. Bristow wrote:
> > Do I need to also add #define BOOST_CXX14_CONSTEXPR in my program or
> elsewhere?
> > (Doing this doesn't change BOOST_CONSTEXPR_OR_CONST from const to
> constexpr)
> >
>
> In develop, you have the option of defining BOOST_MSVC_CXX11_CONSTEXPR.
>

+1.

You might want to read the thread "[config] Changes needed for VC++ 2015
Update 3?" if you have not already done so.

Please file a MSVC bug report if you hit any C++11 constexpr bugs in the
Update 3 RC. They giving very high priority to C++11 bugs affecting Boost
code. They would like us to be able to turn BOOST_NO_CXX11_CONSTEXPR off
for Update 3.

--Beman

[Paul A. Bristow]

> -----Original Message-----
> From: Boost [mailto:boost-...@lists.boost.org] On Behalf Of Beman Dawes
> Sent: 11 June 2016 17:06
> To: Boost Developers List
> Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)
>
> On Sat, Jun 11, 2016 at 11:57 AM, Glen Fernandes <glen.fe...@gmail.com>
> wrote:
>
> > On Sat, Jun 11, 2016 at 11:41 AM, Paul A. Bristow wrote:
> > > Do I need to also add #define BOOST_CXX14_CONSTEXPR in my program or
> > elsewhere?
> > > (Doing this doesn't change BOOST_CONSTEXPR_OR_CONST from const to
> > constexpr)
> > >
> >
> > In develop, you have the option of defining BOOST_MSVC_CXX11_CONSTEXPR.
> >
>
> +1.
>
> You might want to read the thread "[config] Changes needed for VC++ 2015
> Update 3?" if you have not already done so.
>
> Please file a MSVC bug report if you hit any C++11 constexpr bugs in the
> Update 3 RC. They giving very high priority to C++11 bugs affecting Boost
> code. They would like us to be able to turn BOOST_NO_CXX11_CONSTEXPR off
> for Update 3.

I'm using a just-fully-updated modular-boost develop branch.

I've re-read

https://groups.google.com/forum/#!topic/boost-developers-archive/yzERahUyJRE

and added either or both

#define BOOST_CXX14_CONSTEXPR
#define BOOST_MSVC_CXX14_CONSTEXPR

but when I hover over

BOOST_CONSTEXPR_OR_CONST

it still shows const rather than constexpr

and I am not getting an (unsuccessful so far) attempt to implement constexpr

1>fixed_point_constexpr.cpp(61): error C2127: 'bn1': illegal initialization of 'constexpr' entity with a non-constant expression

that would be shown if I was misunderstanding the meaning of the hover display.

So I'm doing something wrong still.

(In case it helps, the code only contains

#include <boost/fixed_point/fixed_point.hpp>
#include <boost/math/special_functions/bernoulli.hpp>

typedef boost::fixed_point::negatable<6u, -25, boost::fixed_point::round::nearest_even>
small_fixed_point_type;

constexpr small_fixed_point_type bn1 = boost::math::bernoulli_b2n<small_fixed_point_type>(1);

I'm hoping, perhaps over-optimistically, for a fixed-point value of ==0.1666667 to be assigned to bn1)

Paul


---
Paul A. Bristow
Prizet Farmhouse
Kendal UK LA8 8AB
+44 (0) 1539 561830

[Paul A. Bristow]

> -----Original Message-----
> From: Boost [mailto:boost-...@lists.boost.org] On Behalf Of Marcel Raad
> Sent: 11 June 2016 16:27
> To: bo...@lists.boost.org
> Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)
>

> pabristow wrote
> > (aside I also tried /std:C++latest but that works for some tasks but
> > failed to compile with odd-looking errors in converter.hpp
> >
> > Error C2518 keyword 'typename' illegal in base class list; ignored
> > \modular-boost\boost\numeric\conversion\detail\converter.hpp 453
> >
> > // Trivial Converter : used when (cv-unqualified) T == (cv-unqualified) S
> > //
> > template
> > <class Traits>
> > struct trivial_converter_impl : public std::unary_function<
> > BOOST_DEDUCED_TYPENAME Traits::argument_type
> >
> > ,BOOST_DEDUCED_TYPENAME Traits::result_type
> > >
> > ,public dummy_range_checker
> > <Traits>
> > {...}
> >
> > So I stopped trying that /std:c++latest option. What else should it do?)
>
> To use /std:C++latest, you have to add _HAS_AUTO_PTR_ETC=1 to the
> preprocessor definitions. Otherwise, there is no std::unary_function.

#define _HAS_AUTO_PTR_ETC 1
// http://lists.boost.org/boost-users/2015/09/84966.php

seems to get rid of my compile failure.

Thanks Paul

[Paul A. Bristow]

> -----Original Message-----
> From: Boost [mailto:boost-...@lists.boost.org] On Behalf Of Paul A. Bristow
> Sent: 13 June 2016 14:55
> To: bo...@lists.boost.org
> Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)
> > -----Original Message-----
> > From: Boost [mailto:boost-...@lists.boost.org] On Behalf Of Beman Dawes
> > Sent: 11 June 2016 17:06
> > To: Boost Developers List
> > Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)
> >
> > On Sat, Jun 11, 2016 at 11:57 AM, Glen Fernandes <glen.fe...@gmail.com>
> > wrote:
> >
> > > On Sat, Jun 11, 2016 at 11:41 AM, Paul A. Bristow wrote:
> > > In develop, you have the option of defining BOOST_MSVC_CXX11_CONSTEXPR.
> > >
> >
> > +1.
> >
> > You might want to read the thread "[config] Changes needed for VC++ 2015
> > Update 3?" if you have not already done so.

> https://groups.google.com/forum/#!topic/boost-developers-archive/yzERahUyJRE

> > Please file a MSVC bug report if you hit any C++11 constexpr bugs in the
> > Update 3 RC. They giving very high priority to C++11 bugs affecting Boost
> > code. They would like us to be able to turn BOOST_NO_CXX11_CONSTEXPR off
> > for Update 3.
>

> I've re-re-read the above and realized that I had assumed (the mother of all snafus) C++14 not C++11

BOOST_MSVC_CXX14_CONSTEXPR

which has no effect, but BOOST_MSVC_CXX11_CONSTEXPR

works as expected (though the compiler is little help in telling just where the constexpr chain is broken :-).

But IMO *we really must know* which of std:c++14 and std::c++lastest (and others including c++11, c++17) are being specified for
the compiler to use.

The compiler version _MSC_FULL_VER = 190024123 does not tell you this - only that it is VS 2015 update 3.

I agree that this is a showstopper for Boost. Has this message got back to Microsoft?

[Marcel Raad]

pabristow wrote

> But IMO *we really must know* which of std:c++14 and std::c++lastest (and
> others including c++11, c++17) are being specified for
> the compiler to use.
>
> The compiler version _MSC_FULL_VER = 190024123 does not tell you this -
> only that it is VS 2015 update 3.

Seems like _MSVC_LANG is 201403 and _HAS_CXX17 is 1 with /std:c++latest.
_MSVC_LANG is 201402 and _HAS_CXX17 is 0 with /std:c++14. See yvals.h.



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Sent from the Boost - Dev mailing list archive at Nabble.com.

[Paul A. Bristow]

> -----Original Message-----
> From: Boost [mailto:boost-...@lists.boost.org] On Behalf Of Marcel Raad
> Sent: 16 June 2016 07:50
> To: bo...@lists.boost.org
> Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)
>

> pabristow wrote
> > But IMO *we really must know* which of std:c++14 and std::c++lastest (and
> > others including c++11, c++17) are being specified for
> > the compiler to use.
> >
> > The compiler version _MSC_FULL_VER = 190024123 does not tell you this -
> > only that it is VS 2015 update 3.
>
> Seems like _MSVC_LANG is 201403 and _HAS_CXX17 is 1 with /std:c++latest.
> _MSVC_LANG is 201402 and _HAS_CXX17 is 0 with /std:c++14. See yvals.h.

Confirmed thanks.

/std:c++latest
Hello Boost!
Platform: Win32
Compiler: Microsoft Visual C++ version 14.0
STL : Dinkumware standard library version 650
Boost : 1.61.0
_MSC_VER =1900
_MSC_FULL_VER=190024123
_MSVC_LANG=201403L
__cplusplus=199711L
_HAS_CXX17=1
_HAS_AUTO_PTR_ETC=0
Processor architecture = (x64)

/std:c++14
Hello Boost!
Platform: Win32
Compiler: Microsoft Visual C++ version 14.0
STL : Dinkumware standard library version 650
Boost : 1.61.0
_MSC_VER =1900
_MSC_FULL_VER=190024123
_MSVC_LANG=201402L
__cplusplus=199711L
_HAS_CXX17=0
_HAS_AUTO_PTR_ETC=1
Processor architecture = (x64)

but confusingly, _MSVC_LANG is not shown as defined using the IDE, but only gets defined and a value assigned when called by, for
example, PRINT_MACRO in

boost_1_61_0_b1\libs\config\test\config_info.cpp

These macro MSVC_LANG and _HAS_CXX17 could usefully be added to config_info.cpp?

This looks workable, if not uber convenient or clear. But things are getting better - slowly...

Paul

---
Paul A. Bristow
Prizet Farmhouse
Kendal UK LA8 8AB
+44 (0) 1539 561830

[Gabriel Dos Reis]

_MSVC_LANG is the macro to hook on. Hopefully, there will be a published
documentation of how to test for _MSC_VER and _MSVC_LANG. The actual value
of _MSVC_LANG may change, but the landmark values to check against are
those defined by the C++ standards for __cplusplus. So you would be testing

_MSVC_LANG > 201402L

for post-C++14 features.


On Thu, Jun 16, 2016 at 3:16 AM, Paul A. Bristow <pbri...@hetp.u-net.com>
wrote:

[Stephan T. Lavavej]

Note that _HAS_CXX17 will be the STL's documented macro for detecting and controlling the library side of C++17 features. We determine its default value from _MSVC_LANG (for C1XX), but we permit it to be overridden in one direction. Namely, you can request C++17 compiler features, but only C++14 library features.

(At the moment, it is technically possible to request the opposite - C++14 compiler with C++17 library - but that will NOT be supported, as we may need to have new library features take dependencies on new compiler features.)

STL

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[Paul A. Bristow]

> -----Original Message-----
> From: Boost [mailto:boost-...@lists.boost.org] On Behalf Of Beman Dawes
> Sent: 11 June 2016 17:06
> To: Boost Developers List

> Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)
>

> You might want to read the thread "[config] Changes needed for VC++ 2015
> Update 3?" if you have not already done so.
>
> Please file a MSVC bug report if you hit any C++11 constexpr bugs in the
> Update 3 RC. They giving very high priority to C++11 bugs affecting Boost
> code. They would like us to be able to turn BOOST_NO_CXX11_CONSTEXPR off
> for Update 3.

Unless I am doing something very silly using Update 3 RC,
it is not possible to declare and initialization any constexpr intermediate variables within a constexpr function.

constexpr int tripled(int n)
{
constexpr int f = 3; // C3250: 'f': declaration is not allowed in 'constexpr' function body
// constexpr_variable_in_function.cpp(35) : error C3249 : illegal statement or sub - expression for 'constexpr' function

return n * f;
}
even using /std:c++latest

Reported as

https://connect.microsoft.com/VisualStudio/feedback/details/2849367

My reading of C++17 draft is that is now an added feature, and this work with GCC 5.3.0 (not even the most recent version).

Lack of this is a showstopper when trying to define any (mathy) function where it is impossible/impractical to provide a single
return statement.

Paul

---
Paul A. Bristow
Prizet Farmhouse
Kendal UK LA8 8AB
+44 (0) 1539 561830

[Billy O'Neal (VC LIBS)]

That is C++14 constexpr; C1XX only supports C++11 constexpr.

Sent from a touchscreen; please excuse the brevity.

On Thu, Jun 23, 2016 at 7:23 AM -0700, "Paul A. Bristow" <pbri...@hetp.u-net.com<mailto:pbri...@hetp.u-net.com>> wrote:

> -----Original Message-----
> From: Boost [mailto:boost-...@lists.boost.org] On Behalf Of Beman Dawes
> Sent: 11 June 2016 17:06
> To: Boost Developers List
> Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)
>
> You might want to read the thread "[config] Changes needed for VC++ 2015
> Update 3?" if you have not already done so.
>
> Please file a MSVC bug report if you hit any C++11 constexpr bugs in the
> Update 3 RC. They giving very high priority to C++11 bugs affecting Boost
> code. They would like us to be able to turn BOOST_NO_CXX11_CONSTEXPR off
> for Update 3.

Unless I am doing something very silly using Update 3 RC,
it is not possible to declare and initialization any constexpr intermediate variables within a constexpr function.

constexpr int tripled(int n)
{
constexpr int f = 3; // C3250: 'f': declaration is not allowed in 'constexpr' function body
// constexpr_variable_in_function.cpp(35) : error C3249 : illegal statement or sub - expression for 'constexpr' function

return n * f;
}
even using /std:c++latest

Reported as

https://na01.safelinks.protection.outlook.com/?url=https%3a%2f%2fconnect.microsoft.com%2fVisualStudio%2ffeedback%2fdetails%2f2849367&data=01%7c01%7cbion%40microsoft.com%7cff91fe2ba4ea4628db3908d39b71f2e8%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=s%2fuVgTFXoqGoAfgDEOSv%2bgo5ZkyDQ%2b03m8B6of9icHw%3d

My reading of C++17 draft is that is now an added feature, and this work with GCC 5.3.0 (not even the most recent version).

Lack of this is a showstopper when trying to define any (mathy) function where it is impossible/impractical to provide a single
return statement.

Paul

---
Paul A. Bristow
Prizet Farmhouse
Kendal UK LA8 8AB
+44 (0) 1539 561830






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[Paul A. Bristow]

> -----Original Message-----
> From: Boost [mailto:boost-...@lists.boost.org] On Behalf Of Billy O'Neal (VC LIBS)
> Sent: 23 June 2016 15:29
> To: bo...@lists.boost.org; bo...@lists.boost.org
> Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)
>

> That is C++14 constexpr; C1XX only supports C++11 constexpr.

I think it may even be a C++17 feature and I have tried /std:c++14 and /std:c++latest to try to enable this.

http://en.cppreference.com/w/cpp/language/constexpr says

the function body must be either deleted or defaulted

* or contain any statements except:*

an asm declaration. Not this
a goto statement. No goto.
a statement with a label other than case and default. NO labels.
a try-block . No trying.
a definition of a variable of non-literal type. Is literal (int, float ...)
a definition of a variable of static or thread storage duration. No static.
a definition of a variable for which no initialization is performed. (variable IS initialized)

But maybe the language lawyers can advise if I am mistaken.

either way, it's a showstopper for taking existing code and making constexpr functions.

But there are more hurdles:
template<typename FloatingPointType>
...
BOOST_CONSTEXPR_OR_CONST bool is_neg = (f < FloatingPointType(0));

and

// Extract the mantissa and exponent.
int exp2 = 0; // Initialize to make constexpr possible.
BOOST_CONSTEXPR_OR_CONST FloatingPointType fp(frexp((!is_neg) ? f : -f, &exp2));

both fail to compile on VS 2015 update 3 RC and GCC 5.8.0.

So there are hoops that look out of reach for now.

Paul

> On Thu, Jun 23, 2016 at 7:23 AM -0700, "Paul A. Bristow" <pbri...@hetp.u-net.com<mailto:pbri...@hetp.u-net.com>>
> wrote:
>
> > -----Original Message-----
> > From: Boost [mailto:boost-...@lists.boost.org] On Behalf Of Beman Dawes
> > Sent: 11 June 2016 17:06
> > To: Boost Developers List
> > Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)
> >
> > You might want to read the thread "[config] Changes needed for VC++ 2015
> > Update 3?" if you have not already done so.
> >
> > Please file a MSVC bug report if you hit any C++11 constexpr bugs in the
> > Update 3 RC. They giving very high priority to C++11 bugs affecting Boost
> > code. They would like us to be able to turn BOOST_NO_CXX11_CONSTEXPR off
> > for Update 3.
>

> Unless I am doing something very silly using VS 2015 Update 3 RC,

[Billy O'Neal (VC LIBS)]

>I think it may even be a C++17 feature and I have tried /std:c++14 and /std:c++latest to try to enable this.

Extended constexpr was a C++14 feature. /std:c++14 and /std:c++latest don't turn this on because C1XX does not have support for it. We implement only C++11 constexpr at this time, which means constexpr functions must be of the form "return expression;".


Billy3
________________________________
From: Boost <boost-...@lists.boost.org> on behalf of Paul A. Bristow <pbri...@hetp.u-net.com>
Sent: Thursday, June 23, 2016 8:46:30 AM
To: bo...@lists.boost.org

Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)

> -----Original Message-----
> From: Boost [mailto:boost-...@lists.boost.org] On Behalf Of Billy O'Neal (VC LIBS)
> Sent: 23 June 2016 15:29
> To: bo...@lists.boost.org; bo...@lists.boost.org
> Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)
>
> That is C++14 constexpr; C1XX only supports C++11 constexpr.

I think it may even be a C++17 feature and I have tried /std:c++14 and /std:c++latest to try to enable this.

https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fen.cppreference.com%2fw%2fcpp%2flanguage%2fconstexpr&data=01%7c01%7cbion%40microsoft.com%7ca35d14a8cc9b416013fd08d39b7d9c7d%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=z1Qv6kRkG8d7dCFKX4Q8DwB2a4wI3S6w9pftYjeDZdI%3d says

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[Niall Douglas]

On 23 Jun 2016 at 17:56, Billy O'Neal (VC LIBS) wrote:

> Extended constexpr was a C++14 feature. /std:c++14 and /std:c++latest
> don't turn this on because C1XX does not have support for it. We
> implement only C++11 constexpr at this time, which means constexpr
> functions must be of the form "return expression;".

I believe typedef/using expressions are permitted before the return
statement. You can also, of course, throw exceptions instead of
returning in C++ 11.

BTW been making heavy use of variable templates in Update 2, apart
from all the ICEs it's a great clutter remover.

Niall

--
ned Productions Limited Consulting
http://www.nedproductions.biz/
http://ie.linkedin.com/in/nialldouglas/

[Paul A. Bristow]

> -----Original Message-----
> From: Boost [mailto:boost-...@lists.boost.org] On Behalf Of Billy O'Neal (VC LIBS)
> Sent: 23 June 2016 18:57
> To: bo...@lists.boost.org
> Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)
>

> >I think it may even be a C++17 feature and I have tried /std:c++14 and /std:c++latest to try to enable this.
>
>
> Extended constexpr was a C++14 feature. /std:c++14 and /std:c++latest don't turn this on because C1XX does not have
> support for it. We implement only C++11 constexpr at this time, which means constexpr functions must be of the form
> "return expression;".

:-( (especially when /std:c++14 or /std:c++latest imply this should be supported).

I look forward to update 4 (or 5...) ;-)

Paul

> > On Thu, Jun 23, 2016 at 7:23 AM -0700, "Paul A. Bristow" <pbri...@hetp.u-net.com<mailto:pbristow@hetp.u-

> a=01%7c01%7cbion%40microsoft.com%7ca35d14a8cc9b416013fd08d39b7d9c7d%7c72f988bf86f141af91ab2d7cd011db47