From 4ff0d30e076d8b4c1a886e7e4ee0b04a26969abb Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 13:24:58 -1000
Subject: [PATCH] Use leak-on-purpose raw pointer for Fan-owned preset modes
 vector

Fan entities live for the entire program lifetime, so the preset
modes vector never needs to be freed. Use a raw pointer (null by
default, allocated on first set_supported_preset_modes() call)
instead of an inline std::vector member.

This saves 24 bytes of RAM per Fan instance for components that
don't use preset modes (binary, bedjet, tuya, etc.).
---
 esphome/components/fan/fan.cpp | 10 +++++-----
 esphome/components/fan/fan.h   | 13 +++++++++----
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/esphome/components/fan/fan.cpp b/esphome/components/fan/fan.cpp
index 659abf70a9..f486c40ca4 100644
--- a/esphome/components/fan/fan.cpp
+++ b/esphome/components/fan/fan.cpp
@@ -148,9 +148,9 @@ const char *Fan::find_preset_mode_(const char *preset_mode) {
 }
 
 const char *Fan::find_preset_mode_(const char *preset_mode, size_t len) {
-  if (preset_mode == nullptr || len == 0)
+  if (preset_mode == nullptr || len == 0 || !this->supported_preset_modes_)
     return nullptr;
-  for (const char *mode : this->supported_preset_modes_) {
+  for (const char *mode : *this->supported_preset_modes_) {
     if (strncmp(mode, preset_mode, len) == 0 && mode[len] == '\0')
       return mode;
   }
@@ -274,10 +274,10 @@ void Fan::save_state_() {
   state.direction = this->direction;
   state.preset_mode = FanRestoreState::NO_PRESET;
 
-  if (this->has_preset_mode()) {
+  if (this->has_preset_mode() && this->supported_preset_modes_) {
     // Find index of current preset mode (pointer comparison is safe since preset is from our vector)
-    for (size_t i = 0; i < this->supported_preset_modes_.size(); i++) {
-      if (this->supported_preset_modes_[i] == this->preset_mode_) {
+    for (size_t i = 0; i < this->supported_preset_modes_->size(); i++) {
+      if ((*this->supported_preset_modes_)[i] == this->preset_mode_) {
         state.preset_mode = i;
         break;
       }
diff --git a/esphome/components/fan/fan.h b/esphome/components/fan/fan.h
index 42999d16f7..2b76fa24da 100644
--- a/esphome/components/fan/fan.h
+++ b/esphome/components/fan/fan.h
@@ -132,10 +132,15 @@ class Fan : public EntityBase {
 
   /// Set the supported preset modes (stored on Fan, referenced by FanTraits via pointer).
   void set_supported_preset_modes(std::initializer_list<const char *> preset_modes) {
-    this->supported_preset_modes_ = preset_modes;
+    if (!this->supported_preset_modes_)
+      this->supported_preset_modes_ =
+          new std::vector<const char *>();  // NOLINT - intentional leak, entity lives forever
+    *this->supported_preset_modes_ = preset_modes;
   }
   void set_supported_preset_modes(const std::vector<const char *> &preset_modes) {
-    this->supported_preset_modes_ = preset_modes;
+    if (!this->supported_preset_modes_)
+      this->supported_preset_modes_ = new std::vector<const char *>();  // NOLINT
+    *this->supported_preset_modes_ = preset_modes;
   }
 
   /// Set the restore mode of this fan.
@@ -179,8 +184,8 @@ class Fan : public EntityBase {
   ESPPreferenceObject rtc_;
   FanRestoreMode restore_mode_;
 
-  /// Preset mode storage — owned by Fan, referenced by FanTraits via pointer.
-  std::vector<const char *> supported_preset_modes_;
+  /// Preset mode storage — allocated on first use, never freed (entity lives forever).
+  std::vector<const char *> *supported_preset_modes_{nullptr};
 
  private:
   const char *preset_mode_{nullptr};