Re: [preprocessor] increase tuple size

From: Edward Diener (eldiener_at_[hidden])
Date: 2019-10-29 02:44:09

On 10/28/2019 8:35 PM, pavel b via Boost-users wrote:
> 
> Hi,
> 
>     No, you should not be changing the limits and doing so will not
>     actually
>     change anything. If you want more than 64 tuple elements you could have
>     a tuple whose elements themselves are tuples. For instance if you
>     wanted
>     256 tuple elements you could program this as a tuple with 64 elements
>     and each of those elements is a tuple with 4 elements. Or if you like a
>     tuple with 16 elements and each of those elements a tuple of 16
>     elements. You get the idea.
> 
> 
> Thank you, good Idea! But in my case it was about the support of an old 
> project, therefore a redesign was not my first choice.
> 
> Unfortunately, there is only little room for improvement. Microsoft C++ 
> compiler, for example, supports only 127 macro arguments. >
> After extending BOOST_PP_VARIADIC_SIZE and BOOST_PP_VARIADIC_SIZE_I in 
> boost/preprocessor/variadic/size.hpp and defining additional 
> BOOST_PP_VARIADIC_ELEM_[64..125] as in preprocessor/tuple/elem.hpp 
> BOOST_PP_TUPLE_SIZE() and BOOST_PP_TUPLE_ELEM() work with up to 126 
> elemnets.

I am not sure what you are saying above. Did you extend the number of 
maximum variadic elements, the number of maximum tuple elements, or both ?

> 
> BOOST_PP_TUPLE_TO_SEQ() uses internal some additional macro parameters, 
> it supports tuples with up to 124 elemrnts after adding 
> BOOST_PP_TUPLE_TO_SEQ_[65..124] similar to preprocessor/tuple/to_seq.hpp

OK.

> 
> No other boost preprocessor macros were changed/tested.
> 
> So after a few simple changes, I have succeeded to extend tuple size 
> from 64 to 124 elements. It seems to work under current MSVC, clang and 
> gcc versions.

You really need to enhance the current tests dealing with variadic data 
and tuples so that you can show that variadic data and tuples with 126 
elements will work properly, in order to verify that your changes work 
in all cases.

Also if you would like to create a PR for your changes I will be glad to 
look at it.

As far as Microsoft C++ only supporting a maximum of 127 macro 
arguments, do you have something which shows that ? It should only 
affect variadic data and not tuples.