From 3d9bf8ee54855396e20b4e221ad28f71625bb76c Mon Sep 17 00:00:00 2001
From: Jakob Widauer <jakob@auterion.com>
Date: Wed, 7 Jun 2023 18:11:01 +0200
Subject: [PATCH] feat: adds front and back methods to Value type (#1458)

Value::front and Value::back
---
 include/json/value.h       | 24 ++++++++++++++++++++++++
 src/test_lib_json/main.cpp | 14 ++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/include/json/value.h b/include/json/value.h
index 15c517e..9a302c1 100644
--- a/include/json/value.h
+++ b/include/json/value.h
@@ -585,6 +585,22 @@ public:
   iterator begin();
   iterator end();
 
+  /// \brief Returns a reference to the first element in the `Value`.
+  /// Requires that this value holds an array or json object, with at least one element.
+  const Value& front() const;
+
+  /// \brief Returns a reference to the first element in the `Value`.
+  /// Requires that this value holds an array or json object, with at least one element.
+  Value& front();
+
+  /// \brief Returns a reference to the last element in the `Value`.
+  /// Requires that value holds an array or json object, with at least one element.
+  const Value& back() const;
+
+  /// \brief Returns a reference to the last element in the `Value`.
+  /// Requires that this value holds an array or json object, with at least one element.
+  Value& back();
+
   // Accessors for the [start, limit) range of bytes within the JSON text from
   // which this value was parsed, if any.
   void setOffsetStart(ptrdiff_t start);
@@ -925,6 +941,14 @@ public:
 
 inline void swap(Value& a, Value& b) { a.swap(b); }
 
+inline const Value& Value::front() const { return *begin(); }
+
+inline Value& Value::front() { return *begin(); }
+
+inline const Value& Value::back() const { return *(--end()); }
+
+inline Value& Value::back() { return *(--end()); }
+
 } // namespace Json
 
 #pragma pack(pop)
diff --git a/src/test_lib_json/main.cpp b/src/test_lib_json/main.cpp
index d0f5364..a6f21c4 100644
--- a/src/test_lib_json/main.cpp
+++ b/src/test_lib_json/main.cpp
@@ -310,10 +310,14 @@ JSONTEST_FIXTURE_LOCAL(ValueTest, arrays) {
   const Json::Value& constArray = array1_;
   JSONTEST_ASSERT_EQUAL(Json::Value(1234), constArray[index0]);
   JSONTEST_ASSERT_EQUAL(Json::Value(1234), constArray[0]);
+  JSONTEST_ASSERT_EQUAL(Json::Value(1234), constArray.front());
+  JSONTEST_ASSERT_EQUAL(Json::Value(1234), constArray.back());
 
   // Access through non-const reference
   JSONTEST_ASSERT_EQUAL(Json::Value(1234), array1_[index0]);
   JSONTEST_ASSERT_EQUAL(Json::Value(1234), array1_[0]);
+  JSONTEST_ASSERT_EQUAL(Json::Value(1234), array1_.front());
+  JSONTEST_ASSERT_EQUAL(Json::Value(1234), array1_.back());
 
   array1_[2] = Json::Value(17);
   JSONTEST_ASSERT_EQUAL(Json::Value(), array1_[1]);
@@ -356,6 +360,8 @@ JSONTEST_FIXTURE_LOCAL(ValueTest, resizePopulatesAllMissingElements) {
   v.resize(n);
   JSONTEST_ASSERT_EQUAL(n, v.size());
   JSONTEST_ASSERT_EQUAL(n, std::distance(v.begin(), v.end()));
+  JSONTEST_ASSERT_EQUAL(v.front(), Json::Value{});
+  JSONTEST_ASSERT_EQUAL(v.back(), Json::Value{});
   for (const Json::Value& e : v)
     JSONTEST_ASSERT_EQUAL(e, Json::Value{});
 }
@@ -406,6 +412,8 @@ JSONTEST_FIXTURE_LOCAL(ValueTest, arrayInsertAtRandomIndex) {
   JSONTEST_ASSERT_EQUAL(Json::Value("index0"), array[0]); // check append
   JSONTEST_ASSERT_EQUAL(Json::Value("index1"), array[1]);
   JSONTEST_ASSERT_EQUAL(Json::Value("index2"), array[2]);
+  JSONTEST_ASSERT_EQUAL(Json::Value("index0"), array.front());
+  JSONTEST_ASSERT_EQUAL(Json::Value("index2"), array.back());
 
   // insert lvalue at the head
   JSONTEST_ASSERT(array.insert(0, str1));
@@ -413,6 +421,8 @@ JSONTEST_FIXTURE_LOCAL(ValueTest, arrayInsertAtRandomIndex) {
   JSONTEST_ASSERT_EQUAL(Json::Value("index0"), array[1]);
   JSONTEST_ASSERT_EQUAL(Json::Value("index1"), array[2]);
   JSONTEST_ASSERT_EQUAL(Json::Value("index2"), array[3]);
+  JSONTEST_ASSERT_EQUAL(Json::Value("index3"), array.front());
+  JSONTEST_ASSERT_EQUAL(Json::Value("index2"), array.back());
   // checking address
   for (Json::ArrayIndex i = 0; i < 3; i++) {
     JSONTEST_ASSERT_EQUAL(vec[i], &array[i]);
@@ -425,6 +435,8 @@ JSONTEST_FIXTURE_LOCAL(ValueTest, arrayInsertAtRandomIndex) {
   JSONTEST_ASSERT_EQUAL(Json::Value("index4"), array[2]);
   JSONTEST_ASSERT_EQUAL(Json::Value("index1"), array[3]);
   JSONTEST_ASSERT_EQUAL(Json::Value("index2"), array[4]);
+  JSONTEST_ASSERT_EQUAL(Json::Value("index3"), array.front());
+  JSONTEST_ASSERT_EQUAL(Json::Value("index2"), array.back());
   // checking address
   for (Json::ArrayIndex i = 0; i < 4; i++) {
     JSONTEST_ASSERT_EQUAL(vec[i], &array[i]);
@@ -438,6 +450,8 @@ JSONTEST_FIXTURE_LOCAL(ValueTest, arrayInsertAtRandomIndex) {
   JSONTEST_ASSERT_EQUAL(Json::Value("index1"), array[3]);
   JSONTEST_ASSERT_EQUAL(Json::Value("index2"), array[4]);
   JSONTEST_ASSERT_EQUAL(Json::Value("index5"), array[5]);
+  JSONTEST_ASSERT_EQUAL(Json::Value("index3"), array.front());
+  JSONTEST_ASSERT_EQUAL(Json::Value("index5"), array.back());
   // checking address
   for (Json::ArrayIndex i = 0; i < 5; i++) {
     JSONTEST_ASSERT_EQUAL(vec[i], &array[i]);