Signal declaration with typed arguments
Signals should be declared with typed arguments. Example: signal player_died(reason: String) and signal item_collected(item_id: String, count: int).
Godot 4 Patterns · all subjects
signals
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Connect signals with explicit Callable
Connect signals using the explicit Callable pattern: signal_owner.player_died.connect(_on_player_died).
Emit signals with .emit()
Emit signals using the .emit() method with arguments: signal_owner.player_died.emit("starvation").
Game-wide signal hub pattern
For game-wide events, use an autoload signal hub to decouple publisher and subscriber. Create game_signals.gd as an autoload extending Node with signal declarations, then connect and emit from anywhere using GameSignals.signal_name.
Signal hub pattern with game_signals autoload
Create a single game_signals autoload to decouple publishers from subscribers entirely. Define all game-wide events in one place: terminal_command_submitted, overlay_requested, overlay_closed, time_advanced, stat_changed, room_changed, achievement_unlocked, sfx_requested, ambient_changed. Anything can publish with GameSignals.signal_name.emit() and subscribe with GameSignals.signal_name.connect(_on_handler).
Diagnose signal connection and emission failures
To verify signal connection succeeded, capture the error: var err := signal.connect(_handler); print("connect err=%d" % err). Test emit separately: signal.emit("test"); print("emitted"). In the handler, log receipt: func _handler(arg) -> void: print("[Handler] received: %s" % arg). If the handler does not print, either the signal did not fire or the connect failed silently (e.g., callable was invalid because the node was freed).