std::span<T,Extent>::operator=

#include <algorithm>
#include <array>
#include <cassert>
#include <cstddef>
#include <iostream>
#include <span>
#include <string_view>
 
void print(std::string_view info = "", std::span <const int> span = {},
 std::size_t extent = 0, std::size_t size_of = 0)
{
 if (span.empty())
 {
 std::cout << info << '\n';
 return;
 }
 
 std::cout << info << '[' << span.size() << "] {";
 std::ranges::for_each (span, [](const int x) { std::cout << ' ' << x; });
 std::cout << " }";
 
 if (extent)
 {
 std::cout << " extent = ";
 if (extent == std::dynamic_extent )
 std::cout << "dynamic";
 else
 std::cout << extent;
 }
 
 if (size_of)
 std::cout << ", sizeof = " << size_of;
 
 std::cout << '\n';
}
 
int main()
{
 std::array <int,6> a1;
 std::array <int,6> a2;
 a1.fill(3);
 a2.fill(4);
 
 auto s1 = std::span (a1);
 auto s2 = std::span (a2);
 print("s1", s1, s1.extent, sizeof(s1));
 print("s2", s2, s2.extent, sizeof(s2));
 
 // Check that assignment performs a shallow copy.
 s1 = s2;
 (s1.data() == s2.data() && s1.size() == s2.size())
 ? print("s1 = s2; is a shallow copy!")
 : print("s1 = s2; is a deep copy!");
 print("s1", s1);
 
 print("Fill s1 with 5:");
 std::ranges::fill (s1, 5);
 // s2 is also 'updated' since s1 and s2 point to the same data
 assert (std::ranges::equal (s1, s2));
 print("s1", s1);
 print("s2", s2);
 print();
 
 int a3[]{1, 2, 3, 4};
 int a4[]{2, 3, 4, 5};
 int a5[]{3, 4, 5};
 
 std::span <int, std::dynamic_extent > dynamic_1{a3};
 std::span <int, std::dynamic_extent > dynamic_2{a4, 3};
 std::span <int, 4> static_1{a3};
 std::span <int, 4> static_2{a4};
 std::span <int, 3> static_3{a5};
 
 print("dynamic_1", dynamic_1, dynamic_1.extent, sizeof(dynamic_1));
 print("dynamic_2", dynamic_2, dynamic_2.extent, sizeof(dynamic_2));
 print("static_1", static_1, static_1.extent, sizeof(static_1));
 print("static_2", static_2, static_2.extent, sizeof(static_2));
 print("static_3", static_3, static_3.extent, sizeof(static_3));
 
 dynamic_1 = dynamic_2; // OK
 dynamic_1 = static_1; // OK
// static_1 = dynamic_1; // ERROR: no match for ‘operator=’
 static_1 = static_2; // OK: same extents = 4
// static_1 = static_3; // ERROR: different extents: 4 and 3
}

s1[6] { 3 3 3 3 3 3 } extent = 6, sizeof = 8
s2[6] { 4 4 4 4 4 4 } extent = 6, sizeof = 8
s1 = s2; is a shallow copy!
s1[6] { 4 4 4 4 4 4 }
Fill s1 with 5:
s1[6] { 5 5 5 5 5 5 }
s2[6] { 5 5 5 5 5 5 }
 
dynamic_1[4] { 1 2 3 4 } extent = dynamic, sizeof = 16
dynamic_2[3] { 2 3 4 } extent = dynamic, sizeof = 16
static_1[4] { 1 2 3 4 } extent = 4, sizeof = 8
static_2[4] { 2 3 4 5 } extent = 4, sizeof = 8
static_3[3] { 3 4 5 } extent = 3, sizeof = 8