Re: Ugly c++ syntax

[user1234 via Digitalmars-d-learn]

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  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.

Re: Ugly c++ syntax

[Rumbu via Digitalmars-d-learn]

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

Re: Ugly c++ syntax

[Ali Çehreli via Digitalmars-d-learn]

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  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

Ugly c++ syntax

[Rumbu via Digitalmars-d-learn]

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


Thanks.