问题

#include <iostream>
#include <ranges>

int main()
{
    for (int num: std::ranges::views::iota(0,5)) {
        std::cout << num << 'n';
    }
    
    for (int i : std::ranges::iota_view{55, 65}) {
        std::cout << i << '\n';
    }
}

CPP Reference
> 2) views::iota(e) 和 views::iota(e, f) 与 iota_view(e) 和 iota_view(e, f) 在任何适当的子表达式 e 和 f 上都是表达式等效的。

是否有使用一个而不是另一个的理由？

如果没有，它们都存在的原因是什么，因为它们都是在 C++20 中引入的吗？

<details>
<summary>英文:</summary>

    #include &lt;iostream&gt;
    #include &lt;ranges&gt;

    int main()
    {
        for (int num: std::ranges::views::iota(0,5)) {
        	std::cout &lt;&lt; num &lt;&lt; &#39;n&#39;;
        }
        
        for (int i : std::ranges::iota_view{55, 65}) {
            std::cout &lt;&lt; i &lt;&lt; &#39;\n&#39;;
        }
    }

[CPP Reference][1]
&gt; 2) `views::iota(e)` and `views::iota(e, f)` are **expression-equivalent** to
&gt; `iota_view(e)` and `iota_view(e, f)` respectively for any suitable
&gt; subexpressions `e` and `f`.

Is there any reason to use one vs the other?

And if not, why do they both exist since they were both introduced in C++20?

[1]: https://en.cppreference.com/w/cpp/ranges/iota_view


</details>


# 答案1
**得分**: 6

`std::ranges::iota_view` 是一种表现得像生成其元素的视图的类型。它必须以某种方式可构造。

`std::views::iota` 是一个辅助自定义点对象，遵循一种模式，当使用时可以产生更高性能/正确的结果。最终它将返回 `std::ranges::iota_view`。所谓的模式是使用 `views::something` 而不是 `ranges::something_view`。

当您嵌套更多适配器时，使用后者可能会产生更好的结果（主要是在编译时）。

一般来说，[更倾向于使用 `views::meow`](https://brevzin.github.io/c++/2023/03/14/prefer-views-meow/)。

<details>
<summary>英文:</summary>

`std::ranges::iota_view` is the type that behaves like a view that generates its elements ad hoc. It must be somehow constructible.

`std::views::iota` is a helper customization point object that follows a pattern which can yield more performant / correct results when used. It will ultimately return `std::ranges::iota_view`. Said pattern is the usage of `views::something` rather than `ranges::something_view`.

When you nest more adaptors together, using the latter may turn out to produce better results (mainly in terms of compile-time).

In general, [prefer `views::meow`](https://brevzin.github.io/c++/2023/03/14/prefer-views-meow/).



</details>