deploy: 4155e2938f

examples/basic_json_view__operator[].cpp

@@ -0,0 +1,44 @@
+#include <iostream>
+#include <nlohmann/json_view.hpp>
+
+using json_document = nlohmann::json_document;
+
+int main()
+{
+    // two user records from a large API response; only the fields that are
+    // actually read are ever touched, and no nlohmann::json tree is built
+    // for the batch
+    json_document batch = json_document::parse(R"(
+      [
+        {"name": "Alice", "email": "alice@example.com", "tags": ["admin", "ops"]},
+        {"name": "Bob", "tags": []}
+      ]
+    )");
+
+    const auto users = batch.root();
+    for (std::size_t i = 0; i < users.size(); ++i)
+    {
+        const auto user = users[i];
+        std::cout << user["name"].materialize().dump();
+
+        // operator[] on a missing object key gives a discarded view -- test
+        // it with is_discarded(). The const overload of json::operator[]
+        // would instead be undefined behavior (guarded by an assertion) for
+        // a missing key
+        const auto email = user["email"];
+        if (!email.is_discarded())
+        {
+            std::cout << " <" << email.materialize().dump() << ">";
+        }
+
+        // the same holds for an array index past the end: a discarded view,
+        // not undefined behavior
+        const auto first_tag = user["tags"][0];
+        if (!first_tag.is_discarded())
+        {
+            std::cout << " #" << first_tag.materialize().dump();
+        }
+
+        std::cout << '\n';
+    }
+}