英文:
How to design a matrix in C++
问题
以下是翻译的代码部分：
我想设计一个矩阵，并希望不能初始化它不当。例如，考虑以下情况：template <typename T, unsigned int R, unsigned int C>class matrix {std::array<T, R*C> _data;//... 构造函数等 ...};现在，我想要一个设计，其中以下操作是可能的，甚至不可能的：auto mat1 = matrix<int, 2, 2>{1, 2, 3, 4};auto mat2 = matrix<int, 2, 2>{1, 2, 3, 4, 5}; // 错误！希望在编译时发生错误auto mat3 = matrix{1, 2, 3, 4}; // matrix<int, 2, 2>;是否有一种优雅的方式来表达这一点？使用构造函数和初始化列表吗？是否可以检查所提供的参数的大小？
英文:
I wanted to design a matrix and wanted that it is not possible to initialize it bad. Consider for example this:
template <typename T, unsigned int R, unsigned int C>class matrix {array<T,R*C> _data;//... Constructors, etc. ...};
Now I would like to have a design where the following is possible or even not:
auto mat1 = matrix<int,2,2>{1, 2, 3, 4};auto mat2 = matrix<int,2,2>{1, 2, 3, 4, 5}; // Error! Hopefully at compile timeauto mat3 = matrix{1,2,3,4}; // matrix<int,2,2>
Is there a elegant way to express that? With Constructors and initializer_list? Is it possible to check the size of provided arguments?
答案1
得分: 3
你可以添加一个接受任意数量参数的构造函数 + 一个推导指南来计算大小：
template<class T, std::size_t R, std::size_t C>struct matrix {// 接受任意类型并进行转发：template<class... Args>matrix(Args&&... args) : _data{std::forward<Args>(args)...} {// 断言大小是否正确：static_assert(sizeof...(Args) == R * C, "初始化无效");}std::array<T, R * C> _data;};// 整数平方根template<std::size_t T, std::size_t N = 0>constexpr std::size_t isqrt() {if constexpr ((N+1) * (N+1) <= T) return isqrt<T, N + 1>();return N;}// 推导指南：template<class T, class... Args>matrix(T&&, Args&&...) ->matrix<T, isqrt<sizeof...(Args) + 1>(), isqrt<sizeof...(Args) + 1>()>;
英文:
You could add a constructor taking an arbitrary amount of arguments + a deduction guide to calculate the sizes:
template <class T, std::size_t R, std::size_t C>struct matrix {// take anything and forward it:template <class... Args>matrix(Args&&... args) : _data{std::forward<Args>(args)...} {// assert that the sizes are correct:static_assert(sizeof...(Args) == R * C, "invalid init");}std::array<T, R * C> _data;};// integer square roottemplate<std::size_t T, std::size_t N = 0>constexpr std::size_t isqrt() {if constexpr ((N+1) * (N+1) <= T) return isqrt<T, N + 1>();return N;}// Deduction guide:template <class T, class... Args>matrix(T&&, Args&&...) ->matrix<T, isqrt<sizeof...(Args) + 1>(), isqrt<sizeof...(Args) + 1>()>;
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