On Mon, 10 Feb 2025, 17:15 Pau Miquel Montequi Hernandez, <
pau.montequi_at_[hidden]> wrote:

> Sorry for my misunderstanding Jonathan,
>
> Indeed "*I don't want to include a header*" is not a justification, it is
> less nowadays if we just "import std;" as a whole.
>

Indeed. I didn't mention that because it's easy and glib to say "modules
fixes that!" but in practice most people aren't able to rely on them yet.



> My point is that something different can be achieved that is not possible
> with the tuple approach, like assigning an explicit type to each symbol, with
> auto […] = std::tuple(…) we are limited to use whatever type the compiler
> deduces which is not always the intention.
>
> The explicitness of for (type_a a = …; type_b b = …; type_c c = …;
> *condition*, *expression*) provides in my opinion more control (I want
> exactly *this type*) and sense of intentionality (I wanted *this* to be
> like *that*), I cannot deny that it is not ideal to pollute the for with
> so much noise though, we can always move variables to the enclosing scope
> if we don't mind giving them a bigger-than-required scope and lifetime or
> use the tuple approach which is less noisy but more broad.
>

If you make the tuple solution more noisy, then you can have the precise
control over types that you want:

for (auto [b,e,o] = tuple<T1,T2,T3>(...); ...)

This gets quite noisy, but it's still something that's possible today, and
uses language features that are useful in more places than just for loops.

And the multiple-init 'for' loop quickly gets noisy too.




> Missatge de Jonathan Wakely <cxx_at_[hidden]> del dia dl., 10 de febr.
> 2025 a les 17:46:
>
>>
>>
>> On Mon, 10 Feb 2025 at 16:03, Pau Miquel Montequi Hernandez <
>> pau.montequi_at_[hidden]> wrote:
>>
>>> You're absolutely right! doing nothing is considerably easier than doing
>>> something :P
>>>
>>> But afaik that's not the criteria to consider or reject proposals, maybe
>>> I'm wrong. Apart from the correct and true fact "*If you include a
>>> header and write the loop 'like this' you can do the same*" is there
>>> any other reason to end the discussion?
>>>
>>
>> I didn't suggest the discussion should end. But I do think that avoiding
>> the need to include a header is not a good justification for a language
>> change.
>>
>> Many C++ features exist precisely so that interesting and useful things
>> can be done in libraries, instead of pushing more and more features into
>> the core language.
>>
>> A language feature to implicitly create a tuple-like type that can
>> initialize a structured binding would allow you to write this without
>> <tuple>:
>>
>> for (auto [b,e,o] = ?(in, in+size, out); ...)
>>
>> but it would also be usable in other places, so would give more benefit
>> than just alternative syntax for `for` loops.
>>
>>
>>
>
> --
> Pablo Miguel Montequi Hernández.
>