https://en.cppreference.com/w/cpp/ranges/iota_view

Allow code like:

```
    for (int i : std::views::iota(1, 10))
        std::cout << i << ' ';
```

Other versions you can create helpers in a similar way.

pon., 10 lut 2025 o 15:18 Pau Miquel Montequi Hernandez via
Std-Proposals <std-proposals_at_[hidden]> napisał(a):
>
> Greetings,
>
> I would like to discuss a revision of the for loop syntax, with the goal of evaluating possible improvements that could enhance its usability.
>
> Common usage of for loops
> The typical use case of a for loop is iterating over a collection of items when the number of iterations is known beforehand. More often than not, this means iterating one-by-one, yet the syntax requires explicitly specifying the increment operation:
>
>> for (int i = 0; i != 42; ++i) // Most of the time, ++i is the expected behavior
>
>
> This raises the question: Can we simplify this pattern while keeping it expressive?
>
> Proposal: defaulting increment and condition
> One approach would be to default the increment operation to pre-increment and assume a typical end condition:
>
>> for (int i = 0; 42) // Implicitly increments i and checks against 42
>
>
> This unsettling syntax leads to another question: can we make it more intuitive?
>
> Alternative syntax inspired by range-for loops
> A syntax resembling C++11's range-for loop can be considered:
>
>> for (int i = 0 : 42) // Iterates from 0 to 42
>> for (int id = get_first_id() : get_last_id())
>> for (auto i = v.rbegin() : v.rend()) // Reverse iteration
>
>
> However, using colon (:) could be problematic since the C++11 range-for loop already follows a specific expansion involving std::begin()/std::end() and unary operator* which may lead to confusion.
>
> Possible concerns and alternative syntax
> The C++11 syntax assumes iterators and unary operator*, while this proposal does not. An alternative syntax can reduce ambiguity:
>
> for (int i = 0 ... 42).
> for (int i = 0 -> 42).
> for (int i = 0 => 42).
> for (int i = 0 <- 42).
> for (int i = 0 <= 42).
>
> Each has different implications, like <-/<= explicitly suggesting reverse iteration.
>
> Also traditional for loops allow variables from the enclosing scope to be accessed on and after the loop, whereas range-based for loops do not, for consistency would the proposed new syntax force the same behaviour?
>
>> int x = 0;
>> for (x : 42) // Error?
>> if (f(x))
>> break;
>>
>> return x; // Error?
>
>
>
> Additional considerations
> Some related improvements could be discussed in parallel:
>
> Allowing a for loop to not require a named variable if it is not going to be used:
>>
>> for (0 : tries) { if (try_to_connect()) return true; }
>
>
> More flexible for loop initialization, allowing multiple init statements:
>>
>> template <auto size>
>> void lcase(const char (&in)[size], char (&out)[size])
>> {
>> for (auto b = in, e = in + size; auto o = out; b != e; ++b, ++o)
>> *o = std::tolower(*b);
>> }
>
>
> Feedback
> I’d like to gather feedback on:
>
> Is simplifying for loops for common use cases desirable?
> Then, an alternative syntax is necessary or adapting C++11’s range-for loop could be a better approach?
> If an alternative syntax is the best approach, will <-/<= and ->/=> provide a good way to express reverse iteration?
> Will it be useful to extend range-for loop reach in order to allow the use of existing variables from the outer scope?
> Any feedback about the additional considerations.
>
>
> Looking forward to your thoughts.
>
> --
> Pablo Miguel Montequi Hernández.
> --
> Std-Proposals mailing list
> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals