• Rumbu (8/8) Feb 05 2021 Can some C++ guru translate in D the template below?
• =?UTF-8?Q?Ali_=c3=87ehreli?= (25/30) Feb 05 2021 With some guesses, I made the following compile:
• Rumbu (5/9) Feb 06 2021 Thank you Ali, but nope, it's "parameter pack folding". This
• user1234 (2/10) Feb 06 2021 modern cpp looks like 10 lines of decl for 1 of actual code.

Rumbu <rumbu rumbu.ro> writes:

Can some C++ guru translate in D the template below?

I gave up after reading a lot, but I didn't manage to understand 
the meaning "&& ..."

template <typename...Tables> static uint8_t 
composite_index_size(Tables const&... tables) { return 
(composite_index_size(tables.size(), 
impl::bits_needed(sizeof...(tables))) && ...) ? 2 : 4; }

Thanks.

=?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:

On 2/5/21 1:10 PM, Rumbu wrote:

 I gave up after reading a lot, but I didn't manage to understand the 
 meaning "&& ..."

I think it's the universal reference.

 template <typename...Tables> static uint8_t composite_index_size(Tables 
 const&... tables) { return (composite_index_size(tables.size(), 
 impl::bits_needed(sizeof...(tables))) && ...) ? 2 : 4; }

With some guesses, I made the following compile:

import std.meta : staticMap;
import std.algorithm : sum;

ubyte composite_index_size(tables...)() {
   return (composite_index_size(tables.length,
                                bits_needed(staticMap!(SizeOf, 
typeof(tables)))))
           ? 2
           : 4;
}

auto composite_index_size(size_t count, size_t total) {
   return 42;
}

enum SizeOf(T) = T.sizeof;

auto bits_needed(size_t[] args...) {
   return args.sum;
}

void main() {
   int[] i;
   double[] d;
   pragma(msg, composite_index_size!(i, d));
}

Ali

Rumbu <rumbu rumbu.ro> writes:

On Saturday, 6 February 2021 at 00:35:12 UTC, Ali Çehreli wrote:
 On 2/5/21 1:10 PM, Rumbu wrote:

 I gave up after reading a lot, but I didn't manage to 
 understand the meaning "&& ..."

 I think it's the universal reference.

Thank you Ali, but nope, it's "parameter pack folding". This 
allows starting with C++ 17 to have recursive templates in one 
liner. Basically, it means "&& template(the rest of arguments)"

https://github.com/microsoft/cppwin32/blob/8a6b2507734dd9e9892059b5794f35109688fc20/cppwin32/winmd/impl/winmd_reader/database.h#L490

user1234 <user1234 12.de> writes:

On Friday, 5 February 2021 at 21:10:21 UTC, Rumbu wrote:
 Can some C++ guru translate in D the template below?

 I gave up after reading a lot, but I didn't manage to 
 understand the meaning "&& ..."

 template <typename...Tables> static uint8_t 
 composite_index_size(Tables const&... tables) { return 
 (composite_index_size(tables.size(), 
 impl::bits_needed(sizeof...(tables))) && ...) ? 2 : 4; }

 Thanks.

modern cpp looks like 10 lines of decl for 1 of actual code.