Allow model holder to release ownership of mujoco structs.

PiperOrigin-RevId: 872242489
Change-Id: I055f54f4e111cc78c489c12d9ae5c02cfb57169d

src/experimental/platform/model_holder.cc

@@ -137,4 +137,22 @@ void ModelHolder::SetLoadError(std::string_view error) {
   error_[sizeof(error_) - 1] = 0;
 }
 
+mjSpec* ModelHolder::ReleaseSpec() {
+  mjSpec* spec = spec_;
+  spec_ = nullptr;
+  return spec;
+}
+
+mjData* ModelHolder::ReleaseData() {
+  mjData* data = data_;
+  data_ = nullptr;
+  return data;
+}
+
+mjModel* ModelHolder::ReleaseModel() {
+  mjModel* model = model_;
+  model_ = nullptr;
+  return model;
+}
+
 }  // namespace mujoco::platform

src/experimental/platform/model_holder.h

@@ -56,6 +56,13 @@ class ModelHolder {
   // Returns the error message if the model failed to load.
   std::string_view error() const { return error_; }
 
+  // Releases ownership of the underlying MuJoCo structures. Callers are now
+  // responsible for calling the appropriate `mj_delete*` function on these
+  // objects.
+  mjSpec* ReleaseSpec();
+  mjData* ReleaseData();
+  mjModel* ReleaseModel();
+
  private:
   ModelHolder() = default;
   void InitFromSpec(mjSpec* spec);