Re: [boost] Variadic append for std::string

Hin Am 03.01.2017 14:20, schrieb Olaf van der Spek:

On Tue, Jan 3, 2017 at 2:19 PM, Christof Donat wrote:

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Am 01.01.2017 00:21, schrieb Andrey Semashev:

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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