add std::expected example

Chapter07/error_handling/app/src/main_expected.cpp

@@ -1,7 +1,7 @@
 #include <cstdint>
 #include <cstdio>
 #include <cstdlib>
-
+#include <expected>
 
 #include <stm32f072xb.h>
 
@@ -10,6 +10,29 @@
 
 #include <retarget.hpp>
 
+struct ble_light_bulb {
+    enum class error {
+        disconnected,
+        timeout
+    };
+    struct config {
+        int r;
+        int g;
+        int b;
+    };
+
+    bool ret_val;
+    std::expected<config, error> get_config() {
+        ret_val = !ret_val;
+        if(ret_val) {
+            return config {10, 20, 30};
+        }
+        else {
+            return std::unexpected(error::timeout);
+        }
+    }
+};
+
 int main()
 {
     hal::init();
@@ -21,6 +44,27 @@ int main()
 
     printf("std::expected example\r\n");
 
+        ble_light_bulb bulb;
+
+    const auto get_config_from_main = [&bulb]() {
+        auto result = bulb.get_config();
+        if(result.has_value()) {
+            auto conf = result.value();
+            printf("Config r %d, g %d, b %d\r\n", conf.r, conf.g, conf.b);
+        } else {
+            auto err = result.error();
+            if(err == ble_light_bulb::error::disconnected) {
+                printf("The bulb is disconnected! \r\n");
+            }
+            else if(err == ble_light_bulb::error::timeout) {
+                printf("Timeout!\r\n");
+            }
+        }
+    };
+
+    get_config_from_main();
+    get_config_from_main();
+
     while(true)
     {
     }

Chapter07/error_handling/app/src/main_optional.cpp

@@ -38,7 +38,7 @@ int main()
 
     printf("std::optional example\r\n");
 
-    auto get_data_from_main = [] () {
+    const auto get_data_from_main = [] () {
       auto result = sensor::get_data();
       if(result) {
           printf("x = %d, y = %d\r\n", (*result).x, (*result).y);