Optimize stateless lambdas to use function pointers (#11551)

esphome/components/sensor/__init__.py

@@ -261,6 +261,7 @@ ExponentialMovingAverageFilter = sensor_ns.class_(
 )
 ThrottleAverageFilter = sensor_ns.class_("ThrottleAverageFilter", Filter, cg.Component)
 LambdaFilter = sensor_ns.class_("LambdaFilter", Filter)
+StatelessLambdaFilter = sensor_ns.class_("StatelessLambdaFilter", Filter)
 OffsetFilter = sensor_ns.class_("OffsetFilter", Filter)
 MultiplyFilter = sensor_ns.class_("MultiplyFilter", Filter)
 ValueListFilter = sensor_ns.class_("ValueListFilter", Filter)
@@ -573,7 +574,7 @@ async def lambda_filter_to_code(config, filter_id):
     lambda_ = await cg.process_lambda(
         config, [(float, "x")], return_type=cg.optional.template(float)
     )
-    return cg.new_Pvariable(filter_id, lambda_)
+    return automation.new_lambda_pvariable(filter_id, lambda_, StatelessLambdaFilter)
 
 
 DELTA_SCHEMA = cv.Schema(

esphome/components/sensor/filter.h

@@ -296,6 +296,21 @@ class LambdaFilter : public Filter {
   lambda_filter_t lambda_filter_;
 };
 
+/** Optimized lambda filter for stateless lambdas (no capture).
+ *
+ * Uses function pointer instead of std::function to reduce memory overhead.
+ * Memory: 4 bytes (function pointer on 32-bit) vs 32 bytes (std::function).
+ */
+class StatelessLambdaFilter : public Filter {
+ public:
+  explicit StatelessLambdaFilter(optional<float> (*lambda_filter)(float)) : lambda_filter_(lambda_filter) {}
+
+  optional<float> new_value(float value) override { return this->lambda_filter_(value); }
+
+ protected:
+  optional<float> (*lambda_filter_)(float);
+};
+
 /// A simple filter that adds `offset` to each value it receives.
 class OffsetFilter : public Filter {
  public: