Allow id() syntax for custom code (#621)

* Allow id() syntax for custom code

* Lint

esphome/components/globals/globals_component.h

@@ -2,6 +2,7 @@
 
 #include "esphome/core/component.h"
 #include "esphome/core/automation.h"
+#include "esphome/core/helpers.h"
 
 namespace esphome {
 namespace globals {
@@ -64,5 +65,7 @@ template<class C, typename... Ts> class GlobalVarSetAction : public Action<Ts...
   C *parent_;
 };
 
+template<typename T> T &id(GlobalsComponent<T> *value) { return value->value(); }
+
 }  // namespace globals
 }  // namespace esphome

esphome/core/helpers.h

@@ -4,6 +4,7 @@
 #include <functional>
 #include <vector>
 #include <memory>
+#include <type_traits>
 
 #include "esphome/core/optional.h"
 #include "esphome/core/esphal.h"
@@ -160,6 +161,11 @@ template<int...> struct seq {};                                       // NOLINT
 template<int N, int... S> struct gens : gens<N - 1, N - 1, S...> {};  // NOLINT
 template<int... S> struct gens<0, S...> { using type = seq<S...>; };  // NOLINT
 
+template<bool B, class T = void> using enable_if_t = typename std::enable_if<B, T>::type;
+
+template<typename T, enable_if_t<!std::is_pointer<T>::value, int> = 0> T id(T value) { return value; }
+template<typename T, enable_if_t<std::is_pointer<T *>::value, int> = 0> T &id(T *value) { return *value; }
+
 template<typename... X> class CallbackManager;
 
 /** Simple helper class to allow having multiple subscribers to a signal.
@@ -192,8 +198,6 @@ struct is_callable  // NOLINT
   static constexpr auto value = decltype(test<T>(nullptr))::value;  // NOLINT
 };
 
-template<bool B, class T = void> using enable_if_t = typename std::enable_if<B, T>::type;
-
 template<typename T, typename... X> class TemplatableValue {
  public:
   TemplatableValue() : type_(EMPTY) {}

tests/custom.h

@@ -3,7 +3,12 @@
 
 class CustomSensor : public Component, public Sensor {
  public:
-  void loop() override { publish_state(42.0); }
+  void loop() override {
+    // Test id() helper
+    float value = id(my_sensor).state;
+    id(my_global_string) = "Hello World";
+    publish_state(42.0);
+  }
 };
 
 class CustomTextSensor : public Component, public TextSensor {

tests/test3.yaml

@@ -246,6 +246,11 @@ binary_sensor:
       - id: custom_binary_sensor
         name: Custom Binary Sensor
 
+globals:
+  - id: my_global_string
+    type: std::string
+    initial_value: '""'
+
 remote_receiver:
   pin: GPIO12
   dump: []