Add ReadAttrVec, ReadAttrArr, ReadAttrStr, and ReadAttrNum to XML utils.

Moving forward, the compiler objects should have encapsulated data, therefore the old ReadAttr* methods are being deprecated as they require raw pointers to read into.

No external changes other than minor improvements to ReadAttr and ReadVector.

PiperOrigin-RevId: 550880401
Change-Id: I632f40322ccd935f9af9b69e66b056c5cda6face

src/xml/xml_util.h

@@ -16,7 +16,9 @@
 #ifndef MUJOCO_SRC_XML_XML_UTIL_H_
 #define MUJOCO_SRC_XML_XML_UTIL_H_
 
-// stl
+#include <array>
+#include <functional>
+#include <optional>
 #include <string>
 #include <vector>
 #include <sstream>
@@ -98,21 +100,60 @@ class mjXUtil {
   // find value in map, return key ("": not found)
   static std::string FindValue(const mjMap* map, int mapsz, int value);
 
-  // read any type from attribute, return number read
+  // if attribute is present, return vector of numerical data
+  template<typename T>
+  static std::optional<std::vector<T>> ReadAttrVec(tinyxml2::XMLElement* elem, const char* attr,
+                                                   bool required = false);
+
+  // if attribute is present, return attribute as a string
+  static std::optional<std::string> ReadAttrStr(tinyxml2::XMLElement* elem, const char* attr,
+                                                bool required = false);
+
+  // if attribute is present, return numerical value of attribute
+  template<typename T>
+  static std::optional<T> ReadAttrNum(tinyxml2::XMLElement* elem, const char* attr,
+                                      bool required = false);
+
+  // if attribute is present, return array of numerical data
+  // N should be small as data is allocated on the stack
+  template<typename T, int N>
+  static std::optional<std::array<T, N>> ReadAttrArr(tinyxml2::XMLElement* elem, const char* attr,
+                                                     bool required = false) {
+    std::array<T, N> arr;
+    int n = 0;
+    if (!ReadAttrValues<T>(elem, attr, [&](int i, T num) { arr[i] = num; n++; }, N)) {
+      throw mjXError(elem, "attribute '%s' has too much data", attr);
+    }
+
+    if (!n) {
+      if (required) {
+        throw mjXError(elem, "required attribute missing: '%s'", attr);
+      } else {
+        return std::nullopt;
+      }
+    }
+
+    if (n < N) {
+      throw mjXError(elem, "attribute '%s' does not have enough data", attr);
+    }
+    return arr;
+  }
+
+  // deprecated: use ReadAttrVec or ReadAttrArr
   template<typename T>
   static int ReadAttr(tinyxml2::XMLElement* elem, const char* attr, const int len,
                       T* data, std::string& text,
                       bool required = false, bool exact = true);
 
-  // read DOUBLE array into C++ vector, return number read
+  // deprecated: use ReadAttrVec
   static int ReadVector(tinyxml2::XMLElement* elem, const char* attr,
                         std::vector<double>& vec, std::string& text, bool required = false);
 
-  // read text attribute
+  // deprecated: use ReadAttrStr
   static bool ReadAttrTxt(tinyxml2::XMLElement* elem, const char* attr, std::string& text,
                           bool required = false);
 
-  // read int attribute
+  // deprecated: use ReadAttrNum
   static bool ReadAttrInt(tinyxml2::XMLElement* elem, const char* attr, int* data,
                           bool required = false);
 
@@ -155,6 +196,11 @@ class mjXUtil {
   // write attribute- keyword
   static void WriteAttrKey(tinyxml2::XMLElement* elem, std::string name,
                            const mjMap* map, int mapsz, int data, int def = -12345);
+
+ private:
+  template<typename T>
+  static bool ReadAttrValues(tinyxml2::XMLElement* elem, const char* attr,
+                             std::function<void (int, T)> push, int max = -1);
 };
 
 #endif  // MUJOCO_SRC_XML_XML_UTIL_H_