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VSignal

A Signals/Slots implementation in D. This implementation is based on the pattern used in ENTT.

A Signal is declared with a delegate:

Signal!(void delegate(int)) sig;

To connect listeners a function pointer, lambda, or delegate can be passed:

void foo(const int) {}

sig.sink.connect!((int) {});
sig.sink.connect!foo;

Forward is applied when possible. However, in D forward treats lvalues as rvalues to fix the ambiguity problem (see here). To go around the situations when trying to move does not work, Signal fallsback to the normal execution for that variable and does a copy.

This can cause a slight bump in the execution speed when using a Signal!(void delegate(int)) and connecting a void delegate(ref int) listener for example.

When connecting lambdas the parameters can be omitted:

sig.sink.connect((_) {});
sig.sink.connect((const _) {});
sig.sink.connect((ref _) {});
sig.sink.connect((ref const _) {});

Signal also accepts connecting listeners from instances:

struct Listener
{
	void opCall(const int) {}
}

Listener listener;

sig.sink.connect!(Listener.opCall)(listener);

As seen above, it is possible to attach an instance to a Slot. This also has some advantages for structuring the code internally. It also allows the user to specify a listener that receives a ref. Take a look at the following:

void bar(immutable ref int, int) {}
immutable int var = 5;

sig.sink.connect!bar(var);
sig.emit(45);

As seen, the Signal is still void delegate(int) however, the Slot that contains the listener bar also has attached the payload var, which will be passed to the function's first argument.

Listener connection must be executed with Sink. As seen throughout this explanation, all examples use sink before connecting a listener. This allows for Signal to be declared privately internally to omit emit functionality to the user. The user receives a Sink a works with it to connect and disconnect listeners. The Sink also returns another data structure to help managing listeners. The Connection structure is returned every time a connection is made. Connection allows the user to break a connection without having to rely on managing Signal or Sink instances.

Signal usage example:

@safe void foo(immutable ref Listener, int) {}
@safe void bar(int) {}

@safe struct Listener
{
	void opCall(const int) {}
}

void main() @safe
{
	Signal!(void delegate(int) @safe) sig;

	// this can be @trusted because sink's lifetime is lower than sig's.
	auto sink = () @trusted { return sig.sink; } ();

	with (sig.sink)
	{

		Listener listener;

		// connecting
		sink.connect!(Listener.opCall)(listener);
		sink.connect!foo(listener);
		sink.connect!bar;
		auto connection = sink.connect!((ref _) {});

		sig.emit(45);

		// disconnect a listener with an instance
		sink.disconnect!(Listener.opCall)(instance);

		// disconnect a listener
		sink.disconnect!bar;

		// disconnect all listeners with an instance
		sink.disconnect(listener);

		// disconnect all listeners
		sink.disconnect();

		// for lambdas the connection must be used
		connection.release();
	}
}

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Contribution:

If you are interested in project and want to improve it, creating issues and pull requests are highly appretiated!