From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Peter Johnson <johnson.peter@gmail.com>
Date: Fri, 3 Apr 2026 22:58:18 -0700
Subject: [PATCH 18/25] Add container functions

---
 json.cpp | 102 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 json.h   |  18 ++++++++++
 2 files changed, 120 insertions(+)

diff --git a/json.cpp b/json.cpp
index 40479bc266390f015e291b737b5751522dac76ac..2307536b15be9aae19da4ec9370a5aa17d5150d1 100644
--- a/json.cpp
+++ b/json.cpp
@@ -606,6 +606,28 @@ json::contains(std::string_view key) const
     return object_value.find(key) != object_value.end();
 }
 
+json*
+json::lookup(std::string_view key)
+{
+    if (!is_object())
+        return nullptr;
+    auto i = object_value.find(key);
+    if (i == object_value.end())
+        return nullptr;
+    return &i->second;
+}
+
+const json*
+json::lookup(std::string_view key) const
+{
+    if (!is_object())
+        return nullptr;
+    auto i = object_value.find(key);
+    if (i == object_value.end())
+        return nullptr;
+    return &i->second;
+}
+
 json&
 json::operator[](size_t index)
 {
@@ -625,6 +647,86 @@ json::operator[](std::string_view key)
     return object_value[key];
 }
 
+json&
+json::at(size_t index) {
+    if (!is_array())
+        ON_LOGIC_ERROR("JSON value is not an array.");
+    return array_value.at(index);
+}
+
+json&
+json::at(std::string_view key) {
+    if (!is_object())
+        ON_LOGIC_ERROR("JSON value is not an object.");
+    return object_value.at(key);
+}
+
+const json&
+json::at(size_t index) const {
+    if (!is_array())
+        ON_LOGIC_ERROR("JSON value is not an array.");
+    return array_value.at(index);
+}
+
+const json&
+json::at(std::string_view key) const {
+    if (!is_object())
+        ON_LOGIC_ERROR("JSON value is not an object.");
+    return object_value.at(key);
+}
+
+json
+json::value(size_t index, json&& default_value) {
+    if (!is_array())
+        ON_LOGIC_ERROR("JSON value is not an array.");
+    if (index < array_value.size())
+        return array_value[index];
+    return default_value;
+}
+
+json
+json::value(std::string_view key, json&& default_value)
+{
+    if (!is_object())
+        ON_LOGIC_ERROR("JSON value is not an object.");
+    auto i = object_value.find(key);
+    if (i != object_value.end())
+        return i->second;
+    return default_value;
+}
+
+void
+json::erase(std::string_view key)
+{
+    if (!is_object())
+        ON_LOGIC_ERROR("JSON value is not an object.");
+    object_value.erase(key);
+}
+
+json&
+json::emplace_back(json&& value)
+{
+    if (!is_array())
+        set_array();
+    array_value.emplace_back(std::move(value));
+    return array_value.back();
+}
+
+bool
+json::empty() const
+{
+    switch (type_) {
+        case Type::Null:
+            return true;
+        case Type::Array:
+            return array_value.empty();
+        case Type::Object:
+            return object_value.empty();
+        default:
+            return false;
+    }
+}
+
 std::string
 json::to_string() const
 {
diff --git a/json.h b/json.h
index fbc3fb959f71f6acc344f26247597959807d23bb..62af49cb18b713304ad95e89c52f5cc5bbc4b626 100644
--- a/json.h
+++ b/json.h
@@ -216,6 +216,9 @@ class json
 
     bool contains(std::string_view) const;
 
+    json* lookup(std::string_view);
+    const json* lookup(std::string_view) const;
+
     void set_array();
     void set_object();
 
@@ -228,6 +231,21 @@ class json
     json& operator[](size_t);
     json& operator[](std::string_view);
 
+    json& at(size_t);
+    json& at(std::string_view);
+
+    const json& at(size_t) const;
+    const json& at(std::string_view) const;
+
+    json value(size_t, json&&);
+    json value(std::string_view, json&&);
+
+    void erase(std::string_view);
+
+    json& emplace_back(json&& value);
+
+    bool empty() const;
+
     operator std::string() const
     {
         return to_string();