1#include <bits/stdc++.h>
 2using namespace std;
 3
 4template<typename T>
 5class Point {
 6    T x;
 7    T y;
 8public:
 9    Point() {}
10    Point(const T &x, const T &y): x(x), y(y) {}
11    Point operator+(const Point &r) const {
12        return Point(x + r.x, y + r.y);
13    }
14    Point operator-(const Point &r) const {
15        return Point(x - r.x, y - r.y);
16    }
17    bool operator==(const Point &r) const {
18        return x == r.x && y == r.y;
19    }
20    T dot(const Point &r) const {
21        return x * r.x + y * r.y;
22    }
23    T cross(const Point &r) const {
24        return x * r.y - y * r.x;
25    }
26};
27
28template<typename T>
29class Line {
30    Point<T> p;
31    Point<T> q;
32public:
33    Line() {}
34    Line(const Point<T> &p, const Point<T> &q): p(p), q(q) {}
35    T getLen() const {
36        Point<T> tmp = p - q;
37        return sqrt(tmp.dot(tmp));
38    }
39};
40
41int main() {
42    Point<double> a(0, 0), b(3, 4);
43    Line<double> line(a, b);
44    cout << line.getLen() << endl;
45    return 0;
46}