Add map from objects names to their index.

Also some minor cleanup of repeated code in user_model.

PiperOrigin-RevId: 589135294
Change-Id: I16f22c4dbdde961cedc042af3bdc9d3577d33459

src/user/user_model.h

@@ -15,6 +15,8 @@
 #ifndef MUJOCO_SRC_USER_USER_MODEL_H_
 #define MUJOCO_SRC_USER_USER_MODEL_H_
 
+#include <functional>
+#include <map>
 #include <string>
 #include <utility>
 #include <vector>
@@ -30,6 +32,10 @@ typedef enum _mjtInertiaFromGeom {
   mjINERTIAFROMGEOM_AUTO          // use only if inertial element is missing
 } mjtInertiaFromGeom;
 
+// TODO: convert mjListKeyMap to mjKeyMap[mjNOBJECT] by adding mjNOBJECT to mjtObj
+typedef std::map<std::string, int, std::less<> > mjKeyMap;
+typedef std::map<std::string, mjKeyMap, std::less<> > mjListKeyMap;
+
 
 
 //---------------------------------- class mjCModel ------------------------------------------------
@@ -286,6 +292,9 @@ class mjCModel {
   std::vector<mjCCamera*> cameras;  // list of cameras
   std::vector<mjCLight*>  lights;   // list of lights
 
+  // map from object names to ids
+  mjListKeyMap ids;
+
   //------------------------ internal variables
   bool hasImplicitPluginElem;     // already encountered an implicit plugin sensor/actuator
   bool compiled;                  // already compiled flag (cannot be compiled again)