add compile-time observer examples

Chapter15/observer/app/src/main_observer_ct.cpp

@@ -0,0 +1,82 @@
+#include <cstdint>
+#include <cstdio>
+
+#include <functional>
+
+#include <stm32f072xb.h>
+
+#include <hal.hpp>
+#include <stm32f0xx_hal_uart.hpp>
+#include <uart_stm32.hpp>
+
+#include <retarget.hpp>
+
+#include "etl/vector.h"
+
+struct display {
+    static void update(float temp) {
+        printf("Displaying temperature %.2f \r\n", temp);
+    }
+};
+
+struct data_sender {
+    static void update(float temp) {
+        printf("Sending temperature %.2f \r\n", temp);
+    }
+};
+
+struct logger {
+    static void update(float temp) {
+        printf("Logging temperature %.2f \r\n", temp);
+    }
+};
+
+template<typename T>
+concept Updatable = requires (T, float f) {
+    { T::update(f) } -> std::same_as<void>; 
+};
+
+template<typename T>
+concept Notifiable = requires (T, float f) {
+    { T::notify(f) } -> std::same_as<void>; 
+};
+
+template <typename... Subs>
+struct publisher {
+    static void notify(float temp) {
+        (call_update_or_notify<Subs>(temp), ...);
+    }
+private:
+    template<typename T>
+    static void call_update_or_notify(float temp) {
+        if constexpr (Updatable<T>) {
+            T::update(temp);
+        } else if constexpr (Notifiable<T>) {
+            T::notify(temp);
+        }
+        else {
+            static_assert(false, "Type is not Updatable or Notifiable");
+        }
+    }
+};
+
+int main()
+{
+    hal::init();
+
+    hal::uart_stm32<hal::stm32::uart> uart(USART2);
+    uart.init();
+
+    retarget::set_stdio_uart(&uart);
+
+    using temp_publisher = publisher<display, data_sender>;
+    temp_publisher::notify(23.47);
+
+    using temp_publisher_new = publisher<temp_publisher, logger>;
+    temp_publisher_new::notify(42.42);
+
+
+    while(true)
+    {
+    }
+}

Chapter15/observer/app/src/main_observer_ct_basic.cpp

@@ -0,0 +1,54 @@
+#include <cstdint>
+#include <cstdio>
+
+#include <functional>
+
+#include <stm32f072xb.h>
+
+#include <hal.hpp>
+#include <stm32f0xx_hal_uart.hpp>
+#include <uart_stm32.hpp>
+
+#include <retarget.hpp>
+
+struct display {
+    static void update(float temp) {
+        printf("Displaying temperature %.2f \r\n", temp);
+    }
+};
+
+struct data_sender {
+    static void update(float temp) {
+        printf("Sending temperature %.2f \r\n", temp);
+    }
+};
+
+struct logger {
+    static void update(float temp) {
+        printf("Logging temperature %.2f \r\n", temp);
+    }
+};
+
+template <typename... Subs>
+struct publisher {
+    static void notify(float temp) {
+        (Subs::update(temp), ...);
+    }
+};
+
+int main()
+{
+    hal::init();
+
+    hal::uart_stm32<hal::stm32::uart> uart(USART2);
+    uart.init();
+
+    retarget::set_stdio_uart(&uart);
+
+    using temp_publisher = publisher<display, data_sender, logger>;
+    temp_publisher::notify(23.47);
+
+    while(true)
+    {
+    }
+}