[select] Eliminate string allocation in state callbacks (#12505)

Co-authored-by: Jonathan Swoboda <154711427+swoboda1337@users.noreply.github.com>

esphome/components/copy/select/copy_select.cpp

@@ -7,7 +7,7 @@ namespace copy {
 static const char *const TAG = "copy.select";
 
 void CopySelect::setup() {
-  source_->add_on_state_callback([this](const std::string &value, size_t index) { this->publish_state(index); });
+  source_->add_on_state_callback([this](size_t index) { this->publish_state(index); });
 
   traits.set_options(source_->traits.get_options());
 

esphome/components/mqtt/mqtt_select.cpp

@@ -21,8 +21,7 @@ void MQTTSelectComponent::setup() {
     call.set_option(state);
     call.perform();
   });
-  this->select_->add_on_state_callback(
-      [this](const std::string &state, size_t index) { this->publish_state(this->select_->option_at(index)); });
+  this->select_->add_on_state_callback([this](size_t index) { this->publish_state(this->select_->option_at(index)); });
 }
 
 void MQTTSelectComponent::dump_config() {

esphome/components/select/automation.h

@@ -8,9 +8,13 @@ namespace esphome::select {
 
 class SelectStateTrigger : public Trigger<std::string, size_t> {
  public:
-  explicit SelectStateTrigger(Select *parent) {
-    parent->add_on_state_callback([this](const std::string &value, size_t index) { this->trigger(value, index); });
+  explicit SelectStateTrigger(Select *parent) : parent_(parent) {
+    parent->add_on_state_callback(
+        [this](size_t index) { this->trigger(std::string(this->parent_->option_at(index)), index); });
   }
+
+ protected:
+  Select *parent_;
 };
 
 template<typename... Ts> class SelectSetAction : public Action<Ts...> {

esphome/components/select/select.cpp

@@ -32,8 +32,7 @@ void Select::publish_state(size_t index) {
   this->state = option;  // Update deprecated member for backward compatibility
 #pragma GCC diagnostic pop
   ESP_LOGD(TAG, "'%s': Sending state %s (index %zu)", this->get_name().c_str(), option, index);
-  // Callback signature requires std::string, create temporary for compatibility
-  this->state_callback_.call(std::string(option), index);
+  this->state_callback_.call(index);
 #if defined(USE_SELECT) && defined(USE_CONTROLLER_REGISTRY)
   ControllerRegistry::notify_select_update(this);
 #endif
@@ -41,7 +40,7 @@ void Select::publish_state(size_t index) {
 
 const char *Select::current_option() const { return this->has_state() ? this->option_at(this->active_index_) : ""; }
 
-void Select::add_on_state_callback(std::function<void(std::string, size_t)> &&callback) {
+void Select::add_on_state_callback(std::function<void(size_t)> &&callback) {
   this->state_callback_.add(std::move(callback));
 }
 

esphome/components/select/select.h

@@ -75,7 +75,7 @@ class Select : public EntityBase {
   /// Return the option value at the provided index offset (as const char* from flash).
   const char *option_at(size_t index) const;
 
-  void add_on_state_callback(std::function<void(std::string, size_t)> &&callback);
+  void add_on_state_callback(std::function<void(size_t)> &&callback);
 
  protected:
   friend class SelectCall;
@@ -111,7 +111,7 @@ class Select : public EntityBase {
     }
   }
 
-  CallbackManager<void(std::string, size_t)> state_callback_;
+  CallbackManager<void(size_t)> state_callback_;
 };
 
 }  // namespace esphome::select