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

Subject: Re: [boost] enabling constexpr with Visual studio 2015 Update 3 (RC)
From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2016-06-23 10:23:14

> -----Original Message-----
> From: Boost [mailto:boost-bounces_at_[hidden]] 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
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