Sandbox/Concepts.cpp

   1 #include "Concepts.h"
   2
   3 #include <iostream>
   4 #include <functional>
   5 #include <cmath>
   6 #include <concepts>
   7 #include <type_traits>
   8 #include <vector>
   9 using namespace std;
  10
  11 // From: "Demo Zoo: Zero Cost Abstractions in C++20, Rust, & Zig": https://www.youtube.com/watch?v=43X9ia-qpds
  12
  13 namespace Concepts
  14 {
  15     template<class Vec>
  16     using Scalar = std::decay_t<decltype(Vec()[0])>;
  17
  18     template<class Vec>
  19     concept FloatVec =
  20         std::floating_point<Scalar<Vec>> &&
  21         requires(Vec vec)
  22         {
  23             { vec.size() } -> std::integral;
  24         };
  25
  26     template<FloatVec Vec>
  27     auto norm(Vec vec) -> Scalar<Vec> // Should be 'norm(const Vec& vec)' but it doesn't work with VS 2019 16.6.3.
  28     {
  29         using Index = decltype(vec.size());
  30         Scalar<Vec> result = 0;
  31         for (Index i = 0; i < vec.size(); i += 1)
  32         {
  33             result += vec[i] * vec[i];
  34         }
  35         return std::sqrt(result);
  36     }
  37
  38     struct Point2
  39     {
  40         float x = 0;
  41         float y = 0;
  42
  43         auto size() -> int {
  44             return 2;
  45         }
  46
  47         auto operator[](int i) const -> float {
  48             return i == 0 ? x : y;
  49         }
  50     };
  51
  52     float norm2(float x, float y)
  53     {
  54         return norm(Point2{ x, y });
  55     }
  56
  57     double norm_nd(const std::vector<double>& a)
  58     {
  59         return norm(a);
  60     }
  61 }
  62
  63 void Concepts::tests()
  64 {
  65     cout << "norm: " << norm_nd({ 1, 2, 3 }) << endl;
  66     cout << "norm: " << norm2(3, 4) << endl;
  67 }