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Subject: Re: [boost] [MPL] A Proposal
From: Bruno Dutra (brunocodutra_at_[hidden])
Date: 2016-02-29 06:45:08

On Feb 29, 2016 05:46, "Andrey Semashev" <andrey.semashev_at_[hidden]> wrote:
> On 2016-02-29 06:48, Edward Diener wrote:
>> On 2/28/2016 7:13 PM, Andrey Semashev wrote:
>>> On Mon, Feb 29, 2016 at 2:17 AM, Bruno Dutra <brunocodutra_at_[hidden]>
>>> wrote:
>>>> Dear Community,
>>> [snip]
>>>> My proposal is to make Metal officially into a new revision of
>>>> Boost.MPL's
>>>> API, essentially MPL2 as the original proposal by Robert Ramey put it,
>>>> merging both into one single TMP library. The idea would be to provide a
>>>> thin proxy for the current Boost.MPL API which would have two backends
>>>> configurable by preprocessor switches: the original implementation and a
>>>> another one based on Metal.
>>> I don't think it needs to be controlled with preprocessor switches. In
>>> fact, it's best to avoid config macros as much as possible because it
>>> complicates the use of the library in other libraries.
>> I disagree with this. Simply because you are compiling with c++11 on up
>> will not necessarily mean that you want to use the Metal additions to
>> Boost.MPL rather than the current Boost.MPL. Certainly the programmer
>> should have a choice even when C++11 is be used in the compilation.
> I don't see a use case where you would want a C++03 implementation on a C++11 capable compiler. On the other hand I can easily see the situation where several libraries using Boost.MPLv2 conflict because they have defined different config macros for it.

On the other hand we don't want to break code that has been working
for a decade just because it happens to depend on a particular
implementation detail that hasn't been ported back from Metal, or
perhaps even due to an unnexpected bug in it. For such odd cases,
there should be a way to override the default behaviour through the
preprocessor and get the code back running, even if temporarily while
the code is amended/bugs are fixed.


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