From c64091519f96c6b691ebde9e59ce2dd836841c02 Mon Sep 17 00:00:00 2001
From: George Beckstein <george.beckstein@gmail.com>
Date: Tue, 23 Feb 2021 16:30:50 -0500
Subject: [PATCH] Implement polymorphism for DigitalIn

---
 drivers/include/drivers/DigitalIn.h           | 18 +++++-
 .../drivers/interfaces/InterfaceDigitalIn.h   | 55 +++++++++++++++++++
 2 files changed, 70 insertions(+), 3 deletions(-)
 create mode 100644 drivers/include/drivers/interfaces/InterfaceDigitalIn.h

diff --git a/drivers/include/drivers/DigitalIn.h b/drivers/include/drivers/DigitalIn.h
index 1dfddcd0cc..5543ec7253 100644
--- a/drivers/include/drivers/DigitalIn.h
+++ b/drivers/include/drivers/DigitalIn.h
@@ -1,5 +1,5 @@
 /* mbed Microcontroller Library
- * Copyright (c) 2006-2019 ARM Limited
+ * Copyright (c) 2006-2020 ARM Limited
  * SPDX-License-Identifier: Apache-2.0
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -19,9 +19,11 @@
 
 #include "platform/platform.h"
 
+#include "interfaces/InterfaceDigitalIn.h"
 #include "hal/gpio_api.h"
 
 namespace mbed {
+
 /**
  * \defgroup drivers_DigitalIn DigitalIn class
  * \ingroup drivers-public-api-gpio
@@ -51,7 +53,11 @@ namespace mbed {
  * }
  * @endcode
  */
-class DigitalIn {
+class DigitalIn
+#ifdef FEATURE_EXPERIMENTAL_API
+    final : public interface::DigitalIn
+#endif
+{
 
 public:
     /** Create a DigitalIn connected to the specified pin
@@ -75,6 +81,13 @@ public:
         gpio_init_in_ex(&gpio, pin, mode);
     }
 
+    /** Class destructor, deinitialize the pin
+     */
+    ~DigitalIn()
+    {
+        gpio_free(&gpio);
+    }
+
     /** Read the input, represented as 0 or 1 (int)
      *
      *  @returns
@@ -92,7 +105,6 @@ public:
      *  @param pull PullUp, PullDown, PullNone, OpenDrain
      */
     void mode(PinMode pull);
-
     /** Return the output setting, represented as 0 or 1 (int)
      *
      *  @returns
diff --git a/drivers/include/drivers/interfaces/InterfaceDigitalIn.h b/drivers/include/drivers/interfaces/InterfaceDigitalIn.h
new file mode 100644
index 0000000000..78374ea1f9
--- /dev/null
+++ b/drivers/include/drivers/interfaces/InterfaceDigitalIn.h
@@ -0,0 +1,55 @@
+/*
+ * Mbed-OS Microcontroller Library
+ * Copyright (c) 2021 Embedded Planet
+ * Copyright (c) 2021 ARM Limited
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License
+ */
+
+#ifndef MBED_INTERFACE_DIGITALIN_H_
+#define MBED_INTERFACE_DIGITALIN_H_
+
+
+namespace mbed {
+
+class DigitalIn;
+
+namespace interface {
+
+#ifdef FEATURE_EXPERIMENTAL_API
+
+// TODO - move method doxygen comments to interface once this polymorphism is mainstream
+
+// Pure interface definition for DigitalIn
+struct DigitalIn {
+    virtual ~DigitalIn() = default;
+    virtual int read() = 0;
+    virtual void mode(PinMode pull) = 0;
+    virtual int is_connected() = 0;
+
+    virtual operator int()
+    {
+        // Underlying implementation is responsible for thread-safety
+        return read();
+    }
+
+};
+#else
+using DigitalIn = ::mbed::DigitalIn;
+#endif /* FEATURE_EXPERIMENTAL_API */
+
+} // namespace interface
+} // namespace mbed
+
+#endif /* MBED_INTERFACE_DIGITALIN_H_ */