add the pushWithCnv method to the HeterogenMap class

examples/hmap_example.cpp

@@ -128,5 +128,31 @@ int main()
     std::println("hmap_move.size() = {}", hmap_move.size());
     std::println("hmap_copy.size() = {}", hmap_copy.size());
 
+    std::println("\n{:*^80}", " hmap with custom conv funcs ");
+
+    hmap.pushWithCnv(
+        "str_cst", std::string{"ABC"}, [&s](std::string const& v) { return s.c_str(); },
+        [&s](const char* p) {
+            s = p;
+            return s;
+        });
+
+    auto ptr = hmap.get<const char*>("str_cst");
+    if (ptr) {
+        std::println("ptr = {}", ptr.value());
+    } else {
+        std::println("cannot get PTR");
+    }
+
+    // std::string pp = "EEEE";
+    // auto err = hmap.set("str_cst", pp.c_str());
+    const char* pp = "EEEE";
+    auto err = hmap.set("str_cst", pp);
+    if (err) {
+        std::println("cannot set 'str_cst'");
+    } else {
+        std::println("s = {}", s);
+    }
+
     return 0;
 }