如何制作跨度跨度

html5 • • 问答

C++20std::span是一个非常好的编程接口。但是似乎没有一种简单的方法来获得跨度。这是我想要做的：

#include <iostream>
#include <span>
#include <string>
#include <vector>

void print(std::span<std::span<wchar_t>> matrix) {
  for (auto const& str : matrix) {
    for (auto const ch : str) {
      std::wcout << ch;
    }
    std::wcout << 'n';
  }
}

int main() {
  std::vector<std::wstring> vec = {L"Cool", L"Cool", L"Cool"};
  print(vec);
}

这不编译。我该怎么做？

回答

为什么不使用一个概念呢？

#include <iostream>
#include <string>
#include <vector>
#include <ranges>

template <class R, class T>
concept Matrix = 
    std::convertible_to<
        std::ranges::range_reference_t<std::ranges::range_reference_t<R>>,
        T>;

void print(Matrix<wchar_t> auto const& matrix) {
    for (auto const& str : matrix) {
        for (auto const ch : str) {
            std::wcout << ch;
        }
        std::wcout << 'n';
    }
}

int main() {
  std::vector<std::wstring> vec = {L"Cool", L"Cool", L"Cool"};
  print(vec);
}

神箭网

感谢Barry使用标准范围库提出上述简化概念。

  • That concept doesn't check anything. Or rather, it's either `true` or ill-formed... which isn't really what you're looking for in a concept: https://godbolt.org/z/oE9secK48
  • And you can rely on `range_reference_t<R>` already requiring `range<R>`, so just this for short: https://godbolt.org/z/EqWW1n6M1
以上是如何制作跨度跨度的全部内容。
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