libcamera: base: signal: Support connecting signals to functors

It can be useful to connect a signal to a functor, and in particular a
lambda function, while still operating in the context of a receiver
object (to support both object-based disconnection and queued
connections to Object instances).

Add a BoundMethodFunctor class to bind a functor, and a corresponding
Signal::connect() function. There is no corresponding disconnect()
function, as a lambda passed to connect() can't be later passed to
disconnect(). Disconnection typically uses disconnect(T *object), which
will cover the vast majority of use cases.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/test/signal.cpp b/test/signal.cpp
index 595782a2..fcf2def1 100644
--- a/test/signal.cpp
+++ b/test/signal.cpp
@@ -191,6 +191,24 @@ protected:
 		signalVoid_.connect(slotStaticReturn);
 		signalVoid_.connect(this, &SignalTest::slotReturn);
 
+		/* Test signal connection to a lambda. */
+		int value = 0;
+		signalInt_.connect(this, [&](int v) { value = v; });
+		signalInt_.emit(42);
+
+		if (value != 42) {
+			cout << "Signal connection to lambda failed" << endl;
+			return TestFail;
+		}
+
+		signalInt_.disconnect(this);
+		signalInt_.emit(0);
+
+		if (value != 42) {
+			cout << "Signal disconnection from lambda failed" << endl;
+			return TestFail;
+		}
+
 		/* ----------------- Signal -> Object tests ----------------- */
 
 		/*
@@ -256,6 +274,27 @@ protected:
 
 		delete slotObject;
 
+		/* Test signal connection to a lambda. */
+		slotObject = new SlotObject();
+		value = 0;
+		signalInt_.connect(slotObject, [&](int v) { value = v; });
+		signalInt_.emit(42);
+
+		if (value != 42) {
+			cout << "Signal connection to Object lambda failed" << endl;
+			return TestFail;
+		}
+
+		signalInt_.disconnect(slotObject);
+		signalInt_.emit(0);
+
+		if (value != 42) {
+			cout << "Signal disconnection from Object lambda failed" << endl;
+			return TestFail;
+		}
+
+		delete slotObject;
+
 		/* --------- Signal -> Object (multiple inheritance) -------- */
 
 		/*