一种值类型的容器迭代器模板 [英] Container Iterator Template for one value type

问题描述

您之前曾帮助过我，所以在这里我再次遇到另一个问题，希望能得到答案.

you helped me before so here I am again with another question in hope for an answer.

我有一个函数，可以处理一系列 std :: complex< float> 值.我最初对函数定义的尝试是

I have a function that processes a range of std::complex<float> values. My initial attempt of a function definition was

// Example 1
using namespace std; // not in original code
Errc const& process(vector<complex<float>>::iterator begin, vector<complex<float>>::iterator end);

但这仅适用于向量，不适用于C样式的数组，std :: arrays，范围等.

This however only works for vectors, not C-style arrays, std::arrays, ranges, etc.

经过一番摆弄，大量的Google和一点点运气之后，我设法构建了这一点:

After some fiddling, lots of Google and a little bit of luck, I managed to construct this:

// Example 2
using namespace std; // not in original code
template<
    template<typename T> class C,
    typename T,
    typename C<T>::iterator iterator
    >
Errc const& process(typename C<T>::iterator begin, typename C<T>::iterator end);

我什至不确定那是否可行，但至少可以编译.我认为它的作用是定义一个函数，该函数处理具有任意值类型的任何容器.这将是一个问题，因为我只能处理std :: complex(或类似的复杂浮点值)，而不能处理例如std :: string.

I am not even sure if that works but it compiles at least. What I think it does, is define a function that processes any container with an arbitrary value type. This would be a problem, as I can only process std::complex (or maybe similar complex floating point values) but not std::string for example.

我想做什么:

// Example 3
using namespace std; // not in original code
template<
    template<typename complex<float>> class C,
    typename C<complex<float>>::iterator iterator
    >
Errc const& process(typename C<complex<float>>::iterator begin, typename C<complex<float>>::iterator end);

但这显然不是实现此目的的方法.我大约60％的人肯定我在示例2中也弄乱了.

But this apparently is not the way to do this. I am about 60% percent sure I also messed something up in example 2.

任何帮助或提示，我们将不胜感激.谢谢

Any help or hints are greatly appreciated. Thank you

推荐答案

您的示例2几乎是正确的

Your example 2 is nearly correct

template<
    template<typename T> class C,
    typename T,
    typename C<T>::iterator iterator // That is wrong
    >
Errc const& process(typename C<T>::iterator begin, typename C<T>::iterator end);

应为:

template<template <typename> class C, typename T>
Errc const& process(typename C<T>::iterator begin, typename C<T>::iterator end);

但是问题在于 C / T 不可推论，您必须这样称呼它:

But issue is that C/T are not deducible, and you have to call it like:

process<std::vector, std::complex<float>>(v.begin(), v.end());

C-array 和 std :: array 与 template< typename>不匹配C类都没有(并且 std :: vector 也具有默认分配器:-/)

And C-array and std::array doesn't match template <typename> class C neither (and std::vector has default allocator too :-/)

更简单

template<typename Iterator>
Errc const& process(Iterator begin, Iterator end);

可能带有一些SFINAE

possibly with some SFINAE

template <typename Iterator,
          std::enable_if_t<std::is_same_v<std::complex<float>,
                                          std::iterator_traits<Iterator>::value_type>, int> = 0>
Errc const& process(Iterator begin, Iterator end);

或C ++ 20要求:

or C++20 requires:

template <typename Iterator>
Errc const& process(Iterator begin, Iterator end)
requires (std::is_same_v<std::complex<float>, std::iterator_traits<Iterator>::value_type);

如果仅需要连续序列，则可以使用 std :: span

If you want only contiguous sequences, you might use std::span

Errc const& process(std::span<std::complex<float>)

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