Re: [boost] C++17 detection

Subject: Re: [boost] C++17 detection
From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2017-09-11 16:43:54

On 11/09/2017 16:58, Robert Ramey via Boost wrote:
> On 9/10/17 12:07 PM, Glen Fernandes via Boost wrote:
>> On Sun, Sep 10, 2017 at 1:30 PM, Robert Ramey via Boost wrote:
>>> How do I get ready for C++17?
>>>
>>> I have a piece of code which requires C++14.  I want to use something 
>>> from
>>> C++17 but I also want my code to work now.  So I have
>>>
>>> #if C++14 being used
>>> namespace std {
>>> // implement C++ function
>>> }
>>
>> Don't define those things inside namespace std. Instead:
> 
> Hmmmm - I've done this from time to time.  Why would this be a bad thing?

Because it can fail. Newer stdlib implementations use inline namespaces 
so you just can't forward declare things in namespace std. You need more 
elaborated tricks:

http://www.boost.org/doc/libs/1_65_1/boost/move/detail/std_ns_begin.hpp

http://www.boost.org/doc/libs/1_65_1/boost/move/detail/std_ns_end.hpp

A Boost.Config or similar library that does this would be useful. That 
way we could forward declare standard classes instead of pulling the 
whole header.

Best,

Ion