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

Subject: Re: [boost] Variadic append for std::string
From: Richard Hodges (hodges.r_at_[hidden])
Date: 2017-01-24 05:29:44

Responses inline.

On 24 January 2017 at 10:45, Christof Donat <cd_at_[hidden]> wrote:

> Hi,
>
> Sorry for the unfinished mail. I just was unable to handle my mail client
> correctly :-(
>
> Am 24.01.2017 10:07, schrieb Richard Hodges:
>
>> It seems to me that since c++17 is going to have string_view, and boost
>> already does, then there should be a to_string_view free function to
>> return
>> the view of a temporary.
>>
>
> But where will the temporary live then? Someone will have to free the
> memory.

Imagine a function:

void foo(std::string_view s);

which we then call with:

foo(join("the answer to life, the universe and everything is: ", hex(42)));

The generator returned by join would stay alive until the end of the
function foo, so there would be no need to construct a string, only to take
a string_view of it. We could use the string_view implicit in the joiner
object. This saves us an allocation and a copy.

>
> basic ADL interface something like this:
>>
>
> I didn't get that part. What exactly does ADL stand for?

ADL stands for Argument Dependent Lookup. It means that when you call a
free function, the namespaces of its arguments are searched for that
function. This means that you can write operator<<, to_string, hash_code
etc in the namespace of your custom object and the compiler will select the
correct one.

It's used a great deal in boost for customisation of structures like
boost::hash

>
>
> Furthermore, since the entire web is now (thankfully) UTF8, I strongly feel
>> that there should be a utf8 version, which accepts wide and narrow strings
>> and emits them correctly.
>>
>
> UTF-8 is 8 bits only. Just some characters take more than a single byte.
> See https://en.wikipedia.org/wiki/UTF-8
>
> Anyway, I agree, that we should have a wide char version as well for
> UTF-16 support.

I have no problem with a u16 version (UTF-16) for the windows crowd and a
u8 version (UTF-8) for everyone else. The standard supports this idea in
its unicode specialisations of std::string - std::u16string and
std::u32string. A utf-8 string is just a std::basic_string<char> with
utf-aware traits type.

>
>
> Christof
>
>
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