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Re: What is the good of new way of coding?

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On Sat, 17 Sep 2022 20:52:05 -0000 (UTC)
Andreas Kempe <kempe@lysator.liu.se> wrote:

> Den 2022-09-17 skrev Bonita Montero <Bonita.Montero@gmail.com>:
> > Am 17.09.2022 um 16:37 schrieb Andreas Kempe:  
> >> Den 2022-09-17 skrev wij <wyniijj2@gmail.com>:  
> >>> I did not update my C++ understanding (probable since C++11) to
> >>> find out I cannot understand what the codes are about !!!
> >>>
> >>> --- frorm https://groups.google.com/g/comp.lang.c++/c/2ebc6ifoPr4
> >>> #include <iostream>
> >>> #include <utility>
> >>>
> >>> using namespace std;
> >>>
> >>> int main()
> >>> {
> >>> auto pow = []<unsigned P>( double b, integral_constant<unsigned,
> >>> P> ) -> double  
> >>> {
> >>> auto unroll = [&]<size_t ... Indices>( index_sequence<Indices
> >>> ...> ) -> double  
> >>> {
> >>> return ((Indices, b) * ...);
> >>> };
> >>> if constexpr( P )
> >>> return unroll( make_index_sequence<P>() );
> >>> else
> >>> return b;
> >>> };
> >>> cout << pow( 2.0, integral_constant<unsigned, 10'000>() ) << endl;
> >>> }
> >>> ------
> >>>
> >>> Question1: What would the code look like if using C++2006 for the
> >>> above 'program'?  
> >> 
> >> As was pointed out, you can't really write that code without
> >> variadic templates. What is does at it's core, if I'm not
> >> mistaken, is expanding
> >> 
> >> 	((Indices, b) * ...)
> >> 
> >> to
> >> 
> >> 	(0, 2.0) * (1, 2.0) * (2, 2.0) * ... * (9999, 2.0)
> >> 
> >> using modern template magic. The comma operator makes the first
> >> index value disappear and we get
> >> 
> >> 	2.0 * 2.0 * 2.0 * ...
> >> 
> >> 10000 times. Writing something that solves the same problem with a
> >> loop could be
> >> 
> >> 	double result = 1;
> >> 	for (size_t i = 0; i < 10000; i++)
> >> 		result *= (i, 2.0);
> >>   
> >>> Question2: What is the good of such way of coding?  
> >> 
> >> I personally don't know. I have still to see an example of a
> >> variadic template application that I think makes sense and makes
> >> the code more readable.  
> >
> > container.emplace*( ... ) is a good example.
> >
> >  
> 
> Ah, I didn't really consider emplace.
> 
> Even though I use it myself and do see the advantage of constructing
> elements in-place in a container to avoid a move, I'm not too sure I
> really find it an improvement when it comes to readability.
> Personally, I find vector.push_back(MyType(arg1, arg2)) clearer when
> reading code. With emplace, I have to jump to the container
> declaration to find what type is being put into it.
> 
> As for the implementation of emplace itself, I can of course not say
> much regarding variadic templates affecting the readability since I
> see no way of implementing the function without them.

Not all types can efficiently move (i.e. move is a copy) or they are
not even copyable ergo the rationale for emplace.

/Flibble

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What is the good of new way of coding? wij <wyniijj2@gmail.com> - 2022-09-17 05:46 -0700
  Re: What is the good of new way of coding? Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-17 15:03 +0200
    Re: What is the good of new way of coding? Muttley@dastardlyhq.com - 2022-09-17 14:50 +0000
      Re: What is the good of new way of coding? Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-17 17:31 +0200
        Re: What is the good of new way of coding? Muttley@dastardlyhq.com - 2022-09-17 15:59 +0000
          Re: What is the good of new way of coding? Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-17 18:03 +0200
            Re: What is the good of new way of coding? Muttley@dastardlyhq.com - 2022-09-17 16:13 +0000
              Re: What is the good of new way of coding? Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-17 18:34 +0200
                Re: What is the good of new way of coding? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-09-17 19:55 +0200
                Re: What is the good of new way of coding? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-09-17 12:03 -0700
                Re: What is the good of new way of coding? Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-18 16:21 +0200
                Re: What is the good of new way of coding? Muttley@dastardlyhq.com - 2022-09-19 08:30 +0000
                Re: What is the good of new way of coding? Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-19 10:37 +0200
                Re: What is the good of new way of coding? Muttley@dastardlyhq.com - 2022-09-19 08:54 +0000
                Re: What is the good of new way of coding? Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-19 11:13 +0200
  Re: What is the good of new way of coding? Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-17 15:23 +0200
    Re: What is the good of new way of coding? Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-17 15:38 +0200
  Re: What is the good of new way of coding? Andreas Kempe <kempe@lysator.liu.se> - 2022-09-17 14:37 +0000
    Re: What is the good of new way of coding? Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-17 16:40 +0200
      Re: What is the good of new way of coding? Andreas Kempe <kempe@lysator.liu.se> - 2022-09-17 20:52 +0000
        Re: What is the good of new way of coding? Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-09-17 22:18 +0100
          Re: What is the good of new way of coding? Mr Flibble <flibble@reddwarf.jmc.corp> - 2022-09-17 22:21 +0100
            Re: What is the good of new way of coding? Andreas Kempe <kempe@lysator.liu.se> - 2022-09-17 21:31 +0000
  Re: What is the good of new way of coding? Muttley@dastardlyhq.com - 2022-09-17 14:52 +0000
    Re: What is the good of new way of coding? Bonita Montero <Bonita.Montero@gmail.com> - 2022-09-17 17:32 +0200

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