Subject: Re: [boost] Variadic append for std::string
From: Christof Donat (cd_at_[hidden])
Date: 2017-01-03 09:16:27
Hin
Am 03.01.2017 14:20, schrieb Olaf van der Spek:
> On Tue, Jan 3, 2017 at 2:19 PM, Christof Donat <cd_at_[hidden]> wrote:
>> Am 01.01.2017 00:21, schrieb Andrey Semashev:
>>>
>>> throw std::runtime_error(format(std::string()) << "Error " << 47);
>>
>>
>> How would that differ from
>>
>> throw std::runtime_error((std::ostringstream{} << "Error " <<
>> 47).str());
>
> Simpler syntax, better performance
I see the chances for better performance, but for the syntax I don't
really see
any remarkable improvements.
If performance matters, I'd try with boost::spirit::karma. The syntax
will be
less concise, but I am not aware of a faster generic solution.
auto message = std::string{10}; // <- preallocate enough memory for
the message
if( !karma::generate(std::begin(message), ascii::space, "Error " <<
karma::uint_, 47) ) {
// formating the error message failed. throw something else.
}
// since this is the exit of the function, the compiler might apply
copy elision.
throw std::runtime_error(message);
If you have multiple places like that in your code, I guess, you'd like
to wrap it
into a generic function and you have a similar API to the "append()"
proposal. Now
I see, how it might be useful, thanks. I think, append() should rely on
karma
generators then, instead of yet another int to string implementation,
because we
only already have five dozens.
Christof