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

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On Sat, 17 Sep 2022 22:18:34 +0100
Mr Flibble <flibble@reddwarf.jmc.corp> wrote:

> 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
> 

To be fair I was talking about containers in general, as far as vector
is concerned the value_type does need to be at least copyable.

/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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