[text_sensor] Use std::array in SubstituteFilter

esphome/components/text_sensor/__init__.py

@@ -123,7 +123,9 @@ async def substitute_filter_to_code(config, filter_id):
         )
         for conf in config
     ]
-    return cg.new_Pvariable(filter_id, substitutions)
+    return cg.new_Pvariable(
+        filter_id, cg.TemplateArguments(len(substitutions)), substitutions
+    )
 
 
 @FILTER_REGISTRY.register("map", MapFilter, cv.ensure_list(validate_mapping))

esphome/components/text_sensor/filter.cpp

@@ -73,20 +73,14 @@ bool PrependFilter::new_value(std::string &value) {
   return true;
 }
 
-// Substitute
-SubstituteFilter::SubstituteFilter(const std::initializer_list<Substitution> &substitutions)
-    : substitutions_(substitutions) {}
-
-bool SubstituteFilter::new_value(std::string &value) {
-  for (const auto &sub : this->substitutions_) {
-    // Compute lengths once per substitution (strlen is fast, called infrequently)
-    const size_t from_len = strlen(sub.from);
-    const size_t to_len = strlen(sub.to);
+// Substitute — non-template helper
+bool substitute_filter_apply(const Substitution *substitutions, size_t count, std::string &value) {
+  for (size_t i = 0; i < count; i++) {
+    const size_t from_len = strlen(substitutions[i].from);
+    const size_t to_len = strlen(substitutions[i].to);
     std::size_t pos = 0;
-    while ((pos = value.find(sub.from, pos, from_len)) != std::string::npos) {
-      value.replace(pos, from_len, sub.to, to_len);
-      // Advance past the replacement to avoid infinite loop when
-      // the replacement contains the search pattern (e.g., f -> foo)
+    while ((pos = value.find(substitutions[i].from, pos, from_len)) != std::string::npos) {
+      value.replace(pos, from_len, substitutions[i].to, to_len);
       pos += to_len;
     }
   }

esphome/components/text_sensor/filter.h

@@ -3,6 +3,8 @@
 #include "esphome/core/defines.h"
 #ifdef USE_TEXT_SENSOR_FILTER
 
+#include <array>
+
 #include "esphome/core/component.h"
 #include "esphome/core/helpers.h"
 
@@ -121,14 +123,25 @@ struct Substitution {
   const char *to;
 };
 
-/// A simple filter that replaces a substring with another substring
-class SubstituteFilter : public Filter {
+/// Non-template helper (implementation in filter.cpp)
+bool substitute_filter_apply(const Substitution *substitutions, size_t count, std::string &value);
+
+/// A simple filter that replaces a substring with another substring.
+/// N is set by code generation to match the exact number of substitutions configured in YAML.
+template<size_t N> class SubstituteFilter : public Filter {
  public:
-  explicit SubstituteFilter(const std::initializer_list<Substitution> &substitutions);
-  bool new_value(std::string &value) override;
+  explicit SubstituteFilter(const std::initializer_list<Substitution> &substitutions) {
+    size_t i = 0;
+    for (const auto &s : substitutions) {
+      if (i >= N)
+        break;
+      this->substitutions_[i++] = s;
+    }
+  }
+  bool new_value(std::string &value) override { return substitute_filter_apply(this->substitutions_.data(), N, value); }
 
  protected:
-  FixedVector<Substitution> substitutions_;
+  std::array<Substitution, N> substitutions_{};
 };
 
 /** A filter that maps values from one set to another