Re: [boost] [metaparse] Practical usefulness

Subject: Re: [boost] [metaparse] Practical usefulness
From: Evgeny Panasyuk (evgeny.panasyuk_at_[hidden])
Date: 2015-06-03 17:32:03

03.06.2015 23:45, Abel Sinkovics:
>>> This approach to write a type-safe printf displays the characters
>>> one-by-one on an output stream. The printf library in Mpllibs does the
>>> validation at compile-time and calls the "unsafe" printf at runtime (and
>>> has therefore no runtime overhead).
>> Well that's assuming that printf() is efficient at runtime.
>> I would like to hope that
>>
>>    string s = "hello" + t + "world";
>>
>> would be more efficient than
>>
>>    string s =
>> wrapper_around_printf_returning_string("hello%sworld",t.c_str());
>>
>> If it isn't, we're in trouble :-)
> Given that the format string is known at compile-time, it should be
> possible to generate "optimal" code for it using a metaprogram. But that
> is significantly more complicated than what safe_printf currently offers.

JFYI, I made small test some time ago with "formatting" stuff at 
compile-time (ad-hoc parsing, without Metaparse).
https://github.com/panaseleus/ctte

Following code:

{
     int counter = 2;
     char character = '!';
     double value = 0.5;

     for_each_part
     (
         auto x,
"val = $value$, cnt = $counter$, ch = $character$, again v=$value$;\n",
         counter, character, value
     )
     {
         print_it(x);
     };
}

Produces identical ASM code to handwritten version:

{
     int counter = 2;
     char character = '!';
     double value = 0.5;

     print_it("val = ");
     print_it(value);
     print_it(", cnt = ");
     print_it(counter);
     print_it(", ch = ");
     print_it(character);
     print_it(", again v=");
     print_it(value);
     print_it(";\n");
}

Best Regards,
Evgeny Panasyuk