std::slice

std::slice::slice

Constructs a new slice.

Parameters

std::slice::start, size, stride

Returns the parameters passed to the slice on construction - start, size and stride respectively.

Parameters

(none)

Return value

The parameters of the slice -- start, size and stride respectively.

Complexity

Constant.

operator==(std::slice)

Checks if the parameters of lhs and rhs - start, size and stride are equal respectively.

This function is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::slice is an associated class of the arguments.

The != operator is synthesized from operator==.

Parameters

Return value

lhs.start() == rhs.start() && lhs.size() == rhs.size() && lhs.stride() == rhs.stride()

Barebones valarray-backed Matrix class with a trace calculating function.

#include <iostream>
#include <valarray>
 
class Matrix
{
 std::valarray <int> data;
 int dim;
public:
 Matrix(int r, int c) : data(r*c), dim(c) {}
 int& operator()(int r, int c) { return data[r * dim + c]; }
 int trace() const { return data[std::slice(0, dim, dim + 1)].sum(); }
};
 
int main()
{
 Matrix m(3, 3);
 int n = 0;
 for (int r = 0; r < 3; ++r)
 for (int c = 0; c < 3; ++c)
 m(r, c) = ++n;
 std::cout << "Trace of the matrix (1,2,3) (4,5,6) (7,8,9) is " << m.trace() << '\n';
}

Output:

Trace of the matrix (1,2,3) (4,5,6) (7,8,9) is 15