std::span::operator=(3)

NAME
std::span::operator= - std::span::operator=

Synopsis
   constexpr span& operator=( const span& other ) noexcept = default; (since C++20)
   Assigns other to *this. This defaulted assignment operator performs a shallow copy
   of the data pointer and the size, i.e., after a call to this function, data() ==
   other.data() and size() == other.size().

Parameters
   other - another span to copy from

Return value
   *this

Example
// Run this code
 #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
 }

Output:
 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

See also
   constructor constructs the span
                 (public member function)
   data direct access to the underlying contiguous storage
                 (public member function)
   size returns the number of elements
                 (public member function)