Re: deprecated: MPL, foreach, typeof, ratio, chrono, assign, more?

From: Robert Ramey (ramey_at_[hidden])
Date: 2024-10-07 16:36:52

On 10/7/24 1:07 AM, John Maddock via Boost wrote:
> 
>>> Should Boost have kept C++03?
>>>
>>
>> This question illustrates a lack of understanding regarding C++ 
>> backwards compatibility.  I have posted an explanation of this at 
>> least a dozen times.  People don't get it.  Here is the LAST time.
>>
>> a) Boost always required that a submission work correctly on the 
>> compiler/library standard existent at the time of submission.
>>
>> b) All subsequent versions of C++ compiler/library must be backwards 
>> compatible with all previous versions.  There have been only a handful 
>> of exceptions to this rule in the last 30 years.

> Actually I disagree, there have been a handful of rather high profile 
> exceptions, which have required quite a bit of maintenance to make code 
> compatible with modern compilers.  The removal of std::iterator and 
> associated base classes being the most painful recent one.

Hmmm - I'm not seeing a disagreement here.  Aside - I always used 
Boost.Iterators so I've never seen this.

>> d) Hence, a program written to be compatible with C++03 is (almost) 
>> guaranteed to function.
>>
>> As far as I know this policy has never changed in the history of 
>> Boost. Probably because it makes no sense to do so.  The recent effort 
>> to "deprecate" support for older compilers was a total waste of time 
>> and effort and added nothing to boost.
> 
> It is certainly true that it's pointless to change code that is working 
> well.  However there are circumstances where some modernization is 
> extremely useful, to pick some random examples from Boost.Math:

Right.  This is the perview of the library maintainer - if there is one.
> 
> * C++11 thread safe static variables are a huge win in code 
> simplification and runtime startup cost (we have lots of tabular data). >
> * Post C++11 meta programming is a lot easier on the compiler (shorter 
> compilation times) than C++03.
> 
> * Post C++17 would let us replace tag dispatching with "if constexpr", 
> which is easier to read and quicker to compile.
> 
> * We do occasionally get bug reports along the lines of "this code is so 
> last century, please modernize".  Unless there is a compelling reason to 
> do so we (or at least I) tend to resist until there is other maintenance 
> going on in that file, but generally removing C++03'isms makes the code 
> easier to grok.

Right.  But all this is outside of the perview and authority of the 
"boost technical leadership" - whatever that is.
> 
> * Younger programmers (the ones we need to encourage to join) don't have 
> a clue about C++03 style code, and just wonder why the heck you're not 
> using lambda's and auto everywhere etc. Eventually my C++03 code will 
> look like F77 does to me: so hopelessly outdated that no sane person 
> would ever want to work on it.   Sad but true!

Fewer younger programmers inspire me these days.
> 
> Best, John.
> 
> 
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