AP_Gripper: add singleton

libraries/AP_Gripper/AP_Gripper.cpp

@@ -70,9 +70,26 @@ const AP_Param::GroupInfo AP_Gripper::var_info[] = {
 
 AP_Gripper::AP_Gripper()
 {
+    if (_s_instance) {
+#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
+        AP_HAL::panic("Too many grippers");
+#endif
+        return;
+    }
+    _s_instance = this;
+
     AP_Param::setup_object_defaults(this, var_info);
 }
 
+/*
+ * Get the AP_Gripper singleton
+ */
+AP_Gripper *AP_Gripper::_s_instance = nullptr;
+AP_Gripper *AP_Gripper::get_instance()
+{
+    return _s_instance;
+}
+
 void AP_Gripper::init()
 {
     // return immediately if not enabled
@@ -133,3 +150,12 @@ PASS_TO_BACKEND(released)
 PASS_TO_BACKEND(grabbed)
 
 #undef PASS_TO_BACKEND
+
+namespace AP {
+
+AP_Gripper *gripper()
+{
+    return AP_Gripper::get_instance();
+}
+
+};

libraries/AP_Gripper/AP_Gripper.h

@@ -23,6 +23,12 @@ class AP_Gripper {
 public:
     AP_Gripper();
 
+    AP_Gripper(const AP_Gripper &other) = delete;
+    AP_Gripper &operator=(const AP_Gripper&) = delete;
+
+    static AP_Gripper *get_instance();
+    static AP_Gripper *_s_instance;
+
     // indicate whether this module is enabled or not
     bool enabled() const { return _enabled; }
 
@@ -74,3 +80,7 @@ private:
 
     AP_Gripper_Backend *backend;
 };
+
+namespace AP {
+    AP_Gripper *gripper();
+};