feat: adds front and back methods to Value type (#1458)

Value::front and Value::back

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)