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

On 12/31/16 20:36, Olaf van der Spek wrote:

On Thu, Dec 29, 2016 at 2:53 PM, Andrey Semashev wrote:

...

I already mentioned in the std-proposals discussion that I don't think formatting should be dealed with by std::string or a function named append().

It'd be helpful if you include *why* you think so..

I've already explained my opinion in the std-proposals discussion. For the sake of completeness, here's a short version: It's simply not std::string's job to do the formatting, IMO. This class should be nothing more than a container of characters (well, it is slightly more now, but I don't consider that a good thing). I guess, that's mostly because I believe one class should be responsible for doing only one thing, and in case of std::string it's storing a string. Adding formatting functionality to std::string would increase the class' bloat in terms of interface and implementation and likely add new dependencies. Though, this is probably not an argument against a separate non-intrusive library. Back to the proposal for Boost, I don't mind if there is a standalone function or library that does the formatting, as long as it offers some advantage over the existing libraries. The proposed function though should not be named `append` IMO because it's not the primary thing the function does. I would expect an `append` algorithm to be generic and compatible with any container, i.e. something that does nothing more than `c.insert(c.end(), x)` or `c.append(x)`, for `x` being every argument in the list of arguments to be appended. I.e. this should work: std::list< double > c{ 1.0, 2.0, 3.0 }; append(c, 10.0, 20.0, 30.0); // calls c.insert() As well as this: std::string s{ "Hello" }; append(s, ", world!", " Happy 2017! :)"); // calls s.append() This, however: append(s, 47); should result not in appending "47" but in appending "/" (a character with code 47). I can see how this could be confusing to someone, but that is what you'd get from calling `s.insert()` manually, and what I'd expect from a function called `append`. If formatting is required I would prefer to be required to spell my intent more clearly, like this: print(s, 47); or: format(s) << 47; Also, I'm not clear enough about the intended use cases of the proposed library. Is the goal just to optimize memory allocation? Is that at all possible when formatting is involved? Would it be better than snprintf into a local buffer? Does the library open new use cases? For example, someone suggested in the std-proposals discussion something similar to this: throw std::runtime_error(format(std::string()) << "Error " << 47); (I wrapped the default-constructed std::string() into format(), because I don't think overloading operator<< for std::string is an acceptable approach for the same reasons I mentioned above.) I think, something with one line capability like that would be useful. Would the library allow something like this? Would the library support targets other than std::string? E.g. would I be able to format into an `std::array< char, 10 >`?