Problem: components can't distinguish custom events

They all look the same, which means they would have to check or poll all
potential sources of change.

Solution: make custom events take an integer tag

I've kept the backwards compatibility by using `-1` for the default custom
event (`Event::Custom`).

include/ftxui/component/event.hpp

@@ -31,6 +31,7 @@ struct Event {
  static Event Special(std::string);
  static Event Mouse(std::string, Mouse mouse);
  static Event CursorReporting(std::string, int x, int y);
+ static Event CustomTagged(int tag);
 
  // --- Arrow ---
  static const Event ArrowLeft;
@@ -74,9 +75,14 @@ struct Event {
 
  const std::string& input() const { return input_; }
 
- bool operator==(const Event& other) const { return input_ == other.input_; }
+ bool operator==(const Event& other) const {
+ return type_ == Type::Custom && other.type_ == Type::Custom ? data_.custom_tag == other.data_.custom_tag : input_ == other.input_;
+ }
  bool operator!=(const Event& other) const { return !operator==(other); }
 
+ int is_custom(int tag) const { return type_ == Type::Custom && data_.custom_tag == tag; }
+ int is_custom() const { return type_ == Type::Custom; }
+
  //--- State section ----------------------------------------------------------
  ScreenInteractive* screen_ = nullptr;
 
@@ -88,6 +94,7 @@ struct Event {
  Character,
  Mouse,
  CursorReporting,
+ Custom,
  };
  Type type_ = Type::Unknown;
 
@@ -99,6 +106,7 @@ struct Event {
  union {
  struct Mouse mouse;
  struct Cursor cursor;
+ int custom_tag;
  } data_ = {};
 
  std::string input_;

src/ftxui/component/event.cpp

@@ -49,6 +49,15 @@ Event Event::CursorReporting(std::string input, int x, int y) {
  return event;
 }
 
+// static
+Event Event::CustomTagged(int tag) {
+ Event event;
+ event.type_ = Type::Custom;
+ event.data_.custom_tag = tag;
+ return event;
+}
+
+
 // --- Arrow ---
 const Event Event::ArrowLeft = Event::Special("\x1B[D"); // NOLINT
 const Event Event::ArrowRight = Event::Special("\x1B[C"); // NOLINT
@@ -84,7 +93,8 @@ const Event Event::Home = Event::Special({27, 91, 72}); // NOLINT
 const Event Event::End = Event::Special({27, 91, 70}); // NOLINT
 const Event Event::PageUp = Event::Special({27, 91, 53, 126}); // NOLINT
 const Event Event::PageDown = Event::Special({27, 91, 54, 126}); // NOLINT
-const Event Event::Custom = Event::Special({0}); // NOLINT
+
+const Event Event::Custom = Event::CustomTagged(-1); // NOLINT
 
 } // namespace ftxui