AP_Button: make singleton

libraries/AP_Button/AP_Button.cpp

@@ -20,6 +20,8 @@
 
 extern const AP_HAL::HAL& hal;
 
+AP_Button *AP_Button::_singleton;
+
 const AP_Param::GroupInfo AP_Button::var_info[] = {
 
     // @Param: ENABLE
@@ -72,6 +74,11 @@ const AP_Param::GroupInfo AP_Button::var_info[] = {
 AP_Button::AP_Button(void)
 {
     AP_Param::setup_object_defaults(this, var_info);
+
+    if (_singleton != nullptr) {
+        AP_HAL::panic("AP_Button must be singleton");
+    }
+    _singleton = this;
 }
 
 /*
@@ -166,3 +173,12 @@ void AP_Button::setup_pins(void)
         hal.gpio->write(pin[i], 1);
     }
 }
+
+namespace AP {
+
+AP_Button &button()
+{
+    return *AP_Button::get_singleton();
+}
+
+}

libraries/AP_Button/AP_Button.h

@@ -28,12 +28,23 @@ public:
     // constructor
     AP_Button(void);
 
+    /* Do not allow copies */
+    AP_Button(const AP_Button &other) = delete;
+    AP_Button &operator=(const AP_Button&) = delete;
+
     static const struct AP_Param::GroupInfo var_info[];
 
     // update button state and send messages, called periodically by main loop
     void update(void);
-    
+
+    static AP_Button *get_singleton(void) {
+        return _singleton;
+    }
+
 private:
+
+    static AP_Button *_singleton;
+
     AP_Int8 enable;
     AP_Int8 pin[AP_BUTTON_NUM_PINS];
 
@@ -65,3 +76,6 @@ private:
     void setup_pins();
 };
 
+namespace AP {
+    AP_Button &button();
+};