[utility] add transfer_view_as

Author: iboB

include/itlib/utility.hpp

@@ -28,7 +28,7 @@
 //
 //                  VERSION HISTORY
 //
-//  1.03 (2025-12-15) Added transfer_view
+//  1.03 (2025-12-15) Added transfer_view/transfer_view_as
 //  1.02 (2023-11-27) Added bit_cast
 //  1.01 (2023-02-08) Added make_nullptr
 //  1.00 (2022-11-28) Initial release
@@ -52,7 +52,7 @@
 // * bit_cast:
 //      A function which allows you to reinterpret_cast between types of the
 //      same size without UB. The same as C++20's std::bit_cast
-// * transfer_view:
+// * transfer_view/transfer_view_as:
 //      A function which allows you to transfer a view (pointer+size) from one
 //      container to another
 //
@@ -96,19 +96,28 @@ constexpr Dst bit_cast(const Src& src) noexcept {
     return dst;
 }
 
-template <typename View, typename SrcContainer, typename TgtContainer>
-View transfer_view(
+template <typename TgtView, typename View, typename SrcContainer, typename TgtContainer>
+TgtView transfer_view_as(
     const View& srcView,
     const SrcContainer& srcContainer,
     TgtContainer& tgtContainer
 ) {
     if (srcView.data() == nullptr) {
-        return View{};
+        return TgtView{};
     }
-    return View(
+    return TgtView(
         tgtContainer.data() + (srcView.data() - srcContainer.data()),
         srcView.size()
     );
 }
 
+template <typename View, typename SrcContainer, typename TgtContainer>
+View transfer_view(
+    const View& srcView,
+    const SrcContainer& srcContainer,
+    TgtContainer& tgtContainer
+) {
+    return transfer_view_as<View>(srcView, srcContainer, tgtContainer);
+}
+
 }

test/t-utility-11.cpp

@@ -62,11 +62,15 @@ TEST_CASE("transfer_view") {
     CHECK(vb.size() == 3);
     CHECK(vb.data() == b.data() + 3);
 
-    vb[0] = 100;
-
     auto cvb = itlib::transfer_view(cva28, a, b);
     CHECK(cvb.size() == 6);
     CHECK(cvb.data() == b.data() + 2);
 
+    auto vb2 = itlib::transfer_view_as<itlib::span<int>>(cva28, a, b);
+
+    vb[0] = 100;
     CHECK(cvb[1] == 100);
+
+    vb2[2] = 200;
+    CHECK(cvb[2] == 200);
 }

test/t-utility-20.cpp

@@ -5,6 +5,8 @@
 #include <doctest/doctest.h>
 #include <vector>
 #include <span>
+#include <string>
+#include <string_view>
 
 TEST_CASE("transfer std::span") {
     std::vector<int> a = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
@@ -25,3 +27,13 @@ TEST_CASE("transfer std::span") {
 
     CHECK(cvb[1] == 100);
 }
+
+TEST_CASE("transfer_view_as") {
+    std::string a = "hello world!!";
+
+    auto hello = std::string_view(a).substr(0, 5);
+    auto hello_span = itlib::transfer_view_as<std::span<char>>(hello, a, a);
+
+    hello_span[0] = 'H';
+    CHECK(hello == "Hello");
+}