Re: [Boost-users] BOOST_PP_SEQ_ENUM troubles

Subject: Re: [Boost-users] BOOST_PP_SEQ_ENUM troubles
From: Cherotek Music (cherotek_at_[hidden])
Date: 2016-07-07 03:04:36

Thanks I see. I'm at work now and can't test it but would replacing the
comma in ARG_PAIR with *BOOST_PP_COMMA help?*

On Thu, Jul 7, 2016 at 1:49 AM, Edward Diener <eldiener_at_[hidden]>
wrote:

> On 7/6/2016 5:27 PM, Cherotek Music wrote:
>
>> Hi,
>> I'm trying to make a macro chain that expands something like this
>>
>> *A, B, C*
>>
>> into something like this
>>
>> *{"A", create<AFile>}, {"B", create<BFile>}, {"C", create<CFile>}*
>>
>> This is what I have come up with
>>
>> *#define FORMATS A, B, C // Add new formats here*
>> *#define SEQ_FORMATS BOOST_PP_VARIADIC_TO_SEQ(FORMATS)*
>> *#define ARG_PAIR(s, data, x) {#x, create<x##File>}*
>> *#define SEQ_ARG_PAIRS BOOST_PP_SEQ_TRANSFORM(ARG_PAIR, ~, SEQ_FORMATS)*
>> *#define ARG_PAIRS BOOST_PP_SEQ_ENUM(SEQ_ARG_PAIRS)*
>>
>> The SEQ_ARG_PAIRS macro does expand into
>>
>> *({"A", create<AFile>}) ({"B", create<BFile>}) ({"C", create<CFile>})*
>>
>> but ARG_PAIRS fails with the following error:
>>
>> test.cpp:20:1: error: macro "BOOST_PP_SEQ_SIZE_0" passed 2 arguments,
>> but takes just 1
>>      ARG_PAIRS
>>  ^
>>     BOOST_PP_SEQ_ENUM_0 ({"B", create<BFile>}) ({"C", create<CFile>})
>> ({"A", create<AFile>}) ({"B", create<BFile>}) ({"C", create<CFile>})
>>
>> Any ideas?
>>
>
> The reason for this is because after your transformation you do not have a
> valid seq anymore for BOOST_PP_SEQ_ENUM. Each seq element must be a one
> element tuple. The comma ( ',' ) in each seq element no longer makes that
> seq element valid, producing a two element tuple. Something like '({"A",
> create<AFile>})' really containes two elements of data, the first one being
> '{"A"' and the second one being 'create<AFile>}'.
>
> thanks a lot
>>
>
>
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users
>