adding missing file

Author: Daniel Lemire

examples/demo.cpp

@@ -0,0 +1,67 @@
+#include "simdjson.h"
+#include "simdjson/json_builder/json_builder.h"
+#include <format>
+
+struct kid {
+  int age;
+  std::string name;
+  std::vector<std::string> toys;
+};
+
+namespace simdjson {
+// Helper code because simdjson does not use reflect for now
+template <typename T>
+  requires(simdjson::json_builder::UserDefinedType<T>)
+simdjson_result<T> tag_invoke(deserialize_tag, std::type_identity<T>,
+                              auto &val) {
+  ondemand::object obj;
+  auto error = val.get_object().get(obj);
+  if (error) {
+    return error;
+  }
+  T t;
+  for (auto keyval : obj) {
+    std::string_view key;
+    SIMDJSON_TRY(keyval.escaped_key().get(key));
+    [:json_builder::expand(std::meta::nonstatic_data_members_of(^T)
+                           ):] >> [&]<auto mem> {
+      if (key == std::string_view(std::meta::identifier_of(mem))) {
+        error = keyval.value().get(t.[:mem:]);
+      }
+    };
+    if (error) {
+      return error;
+    }
+  }
+  return t;
+}
+
+} // namespace simdjson
+
+/**
+
+I am 12 years old
+I have a car
+I have a ball
+My name is John
+My JSON is {"age":12,"name":"John","toys":["car","ball"]}
+
+*/
+void demo() {
+  simdjson::padded_string json_str =
+      R"({"age": 12, "name": "John", "toys": ["car", "ball"]})"_padded;
+  simdjson::ondemand::parser parser;
+  auto doc = parser.iterate(json_str);
+  kid k = doc.get<kid>();
+  std::print("I am {} years old\n", k.age);
+  for (const auto &toy : k.toys) {
+    std::print("I have a {}\n", toy);
+  }
+  std::print("My name is {}\n", k.name);
+
+  std::print("My JSON is {}\n", simdjson::json_builder::to_json_string(k));
+}
+int main() {
+  demo();
+  return EXIT_SUCCESS;
+}